Interactive FAQ

  • General
  • Analytical
  • Chemistry
  • Life Science
  • Labware

  • Ordering
  • Shipping / Delivery
  • Documentation
  • Regulatory
  • Storage
  • Packaging / Labeling
  • Solubility / Stability
Why are some items only available in the UK?
As a result of export restrictions, or transport regulations some items that are manufactured in the USA are not able to be shipped to other countries and so are not available to customers in the UK only. These items continue to be listed on the UK website, but with no pricing or availability. They may also be listed in the printed catalogues with availability indicated as enquire (since regulations may change).
Why are products discontinued and how can I find alternatives?
Products are discontinued for a variety of reasons. It may be that we are experiencing problems with sourcing or identifying a supplier for a chemical. We may have experienced problems with manufacture or packaging of a product. Alternatively a product may be discontinued as a result of low sales, if it is not financially viable, or as a result of changes in transport, storage or other regulations relating to a product. Discontinued items may continue to be listed on our website for some time after discontinuation. Often a suggested alternative will be indicated on our website and ordering systems. A search with the CAS number of the original product on our website may identify an alternative product of the same chemical nature. Please contact us if you would like some assistance in identifying a product.

A guide to searching on our website can be found here

If you would like some assistance in identifying a product, please contact Technical Services Email: Technical Service.
Can I buy the individual parts included in kits separately?
Many of our kit products are manufactured and put together in the other locations. For this reason the individual components may not available in the UK. Please contact us if you have a specific enquiry Email: Technical Service.
Can I get samples for products?
We are not able to offer any smaller sample than the smallest pack size listed for a catalogue item. We may be able to offer a discount on your first purchase of an item if some commitment to purchasing larger amounts, on a successful trial, can be provided. Some products do have sample pack sizes available. Samples would normally be arranged, through the local account manager. To request that an account manager contact you, please Email: Technical Service.
How do I know what grade of product to choose?
Information on the different grades of products that are offered by us and what applications they are suitable for, may be found here. This is intended as a guide and some testing of product and batch suitability may be required depending on the intended application.

Where can I order a catalogue?
You can either send an email to with your account details and or delivery address indicating the catalogues and other literature that you wish to receive, or you can use the link below to request catalogues and literature on our website.
Please find a link to the official terms and conditions of sale shown on our website.
What if I can’t find the product I am looking for?
We would recommend using the CAS number (Chemical Abstracts Service registry number), for a chemical, as a search term, when searching on our website. The CAS number is a unique identifying number for the chemical and overcomes problems that can arise as a result of a chemical being known by different names. If the product that you are looking for is not identified on searching with a CAS number then it is fairly certain that we do not have that material available to offer from our current range of catalogue items.

Searching for products using the structure of the chemical is also possible on our website

There is also a tutorial on searching for products, available, here

If a particular chemical that you require is not available from our catalogue, then we may be able to source this product for you. Our Chemical Sourcing team can help you with the specification and packaging format you require. Click here to find out more.

Alternatively, the website Can be used to identify alternative suppliers.

What are the terms and conditions of sale?
Official terms and conditions of sale, shown on our website.
Do prices include VAT?
No, all prices, listed in our catalogues and on our website, are excluding VAT.
How do I request a quote?
You can request a quotation by contacting our customer services team either by phone FREEPHONE 0800 717181 or by Email:
Can I get a discount for Bulk ordering?
We would consider a purchase of ~10-20 times the largest catalogue pack size of an item to be a bulk purchase, and may be able to offer better pricing for such an order. Please contact SAFC to request a quotation for bulk ordering of chemicals. Email:

Can I order online?
It is possible to set up internet ordering, however you will need to create a profile on our website (register your details), and link this to an existing account. Please contact our ecommerce team for more details and assistance. Email:

How do I set up an account?
To set up a new account please contact and we will send you a New Account Application Form.
Can I track my order online? orders can be tracked online. In order to do this you will need to register your details and set up a profile on our website here If you need further assistance please contact our ecommerce team. Email:

How long can I expect to wait before a product is delivered?
Items that are in stock in the UK will be received by customers in the UK, next day in >90% of cases. Where items are not in stock in the UK they may be sent from another European warehouse in which case you might expect delivery in 3-5 working days.

Items indicated as 'hazardous for transport' may take longer than this. Items restricted to transport by sea freight take 2-3 weeks from Europe or 6-8 weeks or more from the USA.

Why are products recommended for storage in the freezer often sent out at room temperature?
In order to provide you with cost savings, items that are recommended for long term storage in the fridge or freezer may well be sent out at ambient temperature, if they are recognised from our product and transport history as being stable at ambient temperature in the short term (8-10 days). If you prefer to receive a product on ice, it is possible to request this through customer services but if this is not standard for the product there may be an additional 'ice' charge for the handling and delivery.

Our 'Official Policy Statement on Shipping' is available through the following link:

What do I do if the product arrives damaged or I have a problem with a product?
If a product arrives damaged or there are problems relating to the ordering or delivery of a product then please contact our customer services department on FREEPHONE 0800 71 71 81 or by Email:
If you have a problem of a more technical nature involving the performance or specifications of a product then please contact Technical Services FREEPHONE  0800 27 25 72 or by Email: Technical Service.

Can I request courier delivery and what is the cost?

It is possible to request courier delivery for a product that would not normally be shipped in this way, but there may be an associated charge for non-standard courier delivery. Please check with our customer services team for more information on FREEPHONE. 0800 71 71 81.
Can I request that a product is shipped on dry ice?
It is possible to request that a product be shipped on dry ice, but if this is not the standard form of delivery for the product, there may be an additional ‘dry ice shipment’ charge applied. Please check with our customer services team for details. FREEPHONE 0800 71 71 81.
Is there a delivery charge on orders?
Items that are delivered through the standard postal system will not attract an additional delivery charge if under the weight of 2kg.
Items delivered by courier will normally incur a delivery charge. It is possible to request that an item is delivered by courier and by a specific time, if required, but there may be additional charges. Please contact our customer services department for more details: FREEPHONE. 0800 71 71 81. Email:
Can I order products to be sent overseas?
Please contact our exports department for information on purchasing products to be sent overseas or email
Can I arrange for products to be delivered to my home address?
We are not able to make deliveries to residential addresses, even if the product is ordered through a business account.
Where can I find a TSE statement for a Sigma-Aldrich product?
We cannot supply TSE statements for catalogue items, but generally offer certificates of origin where available, which state the general method of manufacture, whether there has been any contact with animal material, and the country of origin.
Our 'Official Certificate of Origin Policy' is available here
Why are the values for percentage purity as determined by Titration sometimes greater than 100%, on the Certificate of Analysis?
Titration measures the ions present in reference to a standard. If other ions (of similar valency) are present in the solution then these may contribute to the value recorded, in addition to the contribution made by the standard itself. The value recorded is greater than that of the standard alone as a result of the titration not being able to differentiate between ions.
Are Safety Datasheets sent out with every product?
Safety Data Sheets will normally be sent with the first order of a product received from us but not subsequently, unless requested. It is possible to request that SDSs are sent out with every order by arrangement with customer services. Alternatively SDSs are generally available on our website, or can be obtained by contacting Technical Services. Email: Technical Service
What documentation is available for products and what information is included in these documents?
A table showing the different types of document that are available for products and the information that is contained in these may be found here.
Can I get Certificates of Analysis sent with every product?
We will not normally send Certificates of Analysis with every delivery of a product but it is possible to request this by arrangement with customer services. FREEPHONE. 0800 71 71 81.
How do I order catalogues or other literature?
To request a catalogue or other literature please send an email to with your account details, delivery address, phone number and email address, indicating the catalogues and other literature that you wish to receive.
Alternatively the link can be used to request catalogues and literature on our website. All fields marked with a star need to be completed on this page.
Can I return unwanted catalogues, for recycling?
It is possible to arrange for catalogues to be collected for recycling. To request collection Email:
How do I change my details or remove my name from the mailing list?
To change your details, remove your name from the mailing list or perhaps request different catalogues or literature Email: . Details for literature requirements can also be requested here.
Where can I find the Aldrich Technical Bulletins?
Aldrich Technical Bulletins are available on our website, here
Do I need a licence to order ethanol?
We offer ethanol at three levels of licence requirement; duty-paid, Industrial Denatured Alcohol (IDA), previously know as Industrial Methylated Spirit (IMS); and Duty-Free Spirit (DFS). For sales of IDA or DFS we will need to see a valid licence or authority from HMRC before supplying the products. Duty-paid ethanol.
All grades of ethanol sold under the Aldrich, Sigma and some SIAL brands are sold as duty-paid. The duty is in the price charged to you as a customer. As duty has been paid, there is no licence requirement and the products can be sold without restriction. Industrial Denatured Alcohol (IDA)
IDA covers a range of ethanol products that have been denatured in various ways to render them undrinkable. We offer only one type of IDA. This is Aldrich product 458600. This material is duty-free. You must have an IDA authorisation to buy this material. The sale and use of this material is governed by The Denatured Alcohol Regulations 2005 (SI 2005 No 1524). Compliance with this legislation can be effected by following the requirements of Customs Notice 473, “Production, Distribution and Use of Denatured Alcohol”. This Notice contains an application form for authorisation. Duty Free Spirit (DFS)
DFS is ethanol that has not been denatured to UK standards. It may be pure ethanol or it may be ethanol that has been denatured, but not in accordance with UK legislation. We offer some SIAL brands as DFS. In order to purchase DFS you must be either registered as a Trade Facility Warehouse, or enduser for manufacture, medical or scientific purposes. To register for TFW status, you will have to contact Her Majesties Royal Customs, directly. If you are an end-user, information and an authority application form can be found in Customs Notice 47, “Duty-free spirits: use in manufacture or for medical or scientific purposes”. Customs Notices can be downloaded from the HMRC website ( Regulations can be downloaded from The Office of Public Sector Information website
Can Sigma Aldrich products be used in clinical applications?
The products offered as catalogue items by Sigma-Aldrich are sold as ‘for laboratory research purposes only’. Our catalogue products are not generally tested, handled or packed under conditions appropriate for clinical or veterinary applications. Where products are indicated as perhaps BP or Ph Eur this is generally indicating that the products have been tested to meet the analytical specifications of pharmacopoeia, but not that they have been handled or packed according to pharmacopoeia. There are a very few exceptions in the catalogue that are specifically indicated as being handled and packed according to Pharmacopoeia. Sigma-Aldrich does however have the capability to manufacture clinical grade products as custom items. Please contact us for a quotation Email:
Are Sigma-Aldrich products suitable for use in food?
Our products are sold for ‘Research only’ and are not suitable for food use. There are, however some products in our ‘flavour and fragrance’ range of products that are food grade certified. Food grade certified products are defined as food grade quality materials packaged in an AIB-audited, ISO 9001:2000 accredited facility. All SAFC food-grade certified products meet the following standards: UNITED STATES: 21 CFR 110 – GMP Standards for Foods
EUROPEAN: 178/2002 – General Food Standards
EUROPEAN 88/388 – Flavouring Standards There are also some products in the Flavour and Fragrance range that are not qualified to be certified as ‘food grade’ even though they are packaged in an AIB-audited, ISO 9001:2000 manufacturing facility. These listings are designated as ‘high quality’ products. These materials may meet the testing requirements of the Food Chemical Codex (FCC) or be identified by the US FDA as Generally Recognised as Safe (GRAS). SAFC makes no claim that these materials are suitable for use as flavourings, and it is the responsibility of the customer to determine if the material is suitable for use in their purposes. More information on the Flavour and Fragrance range of products, can be found here
Can I see the ISO certificates for Sigma-Aldrich manufacturing sites?
ISO certificates relating to the various Sigma-Aldrich Manufacturing sites Worldwide are available here
What is the procedure for ordering legally restricted or controlled products?
To order Scheduled or Controlled items you will need to provide the following:
  • A hard copy of your order
  • An End User Declaration Form
  • Appropriate Licences
You will be advised of the need for End User Declaration Forms and relevant Licences when placing the order for a product. More information on Customer Declaration Forms may be found here
Will I be informed if there are changes to the specification, method of manufacture or supplier of a product that I order regularly?
If you require notification when changes are made to the specification of a product, or when there are changes to the method of manufacturer/supplier for a product,‘change control notification’ can be set up, by arrangement with our quality assurance team. Email: We will not notify customers of every change regarding a product unless change control is set up.
Will I be informed if a problem is identified with a product that I have ordered?
If, as part of our ongoing quality review program, it is identified that a product is not meeting specification, then a recall of the product may be initiated. If a particular batch of a product is recalled then all orders, where the affected batch was sent, will be identified, and the persons receiving this material contacted to advise on the nature of the problem, and agree on an appropriate resolution
Can I obtain the testing methods used by Sigma-Aldrich in quality control?
We are able to provide our quality control testing methods in many cases, but we may need to know why the method is being requested and in some cases will request a lot number for the material that you are working with. Please contact Technical Services for assistance. Email: Technical Service
Enzyme assay details, are available in our enzyme explorer facility, here
What temperature should I store my product at?
The temperature at which a product should be stored will generally be indicated on the label, of the packaging in which the product is supplied. The appropriate storage temperature and conditions may also be indicated on the Safety Data Sheet, Product Information Sheet, Product Listing and also may be on the Specification or Certificate of Analysis.
What temperature is room temperature?
  • Ambient Storage
Many Sigma-Aldrich products may be stored under ambient or uncontrolled conditions. Historically products that are suitable for ambient storage may have labeling that indicates room temperature (RT). This label claim is being phased out and all products that either have no recommendation regarding storage or RT may be stored under ambient, that is uncontrolled, temperature conditions. Please note best practice; avoid direct sunlight during long-term storage due to the temperature elevation this causes.
  • Controlled Storage
Controlled Refrigerator/Cooler
For Sigma-Aldrich products where long-term storage is advised as refrigerator/cooler, our labels indicate 2 to 8 degrees C. This matches the recommended range indicated in the USP as refrigerator (36 deg F to 46 deg F).
  • Controlled Freezer
For Sigma-Aldrich products where long-term storage is advised as freezer, our labels indicate -20 degrees C. Typically, freezer facilities that are used to store these products are thermostatically temperature controlled to within -10 to -25 degrees C. This matches the recommended range indicated in the USP as freezer.
  • Controlled Ultracold Freezer
For Sigma-Aldrich products where the long-term storage is advised as ultracold, our labels indicate -70 degrees C. Typically, ultracold facilities that are used to store these products are thermostatically temperature controlled to within -60 to -100 degrees C.
  • Storage Conditions - Summary
Recommended long-term storage as indicated in Sigma-Aldrich publications and product labels are as
• 2 to 8 degrees C Refrigerator/cooler
• -20 degrees C Freezer implies -10 to –25 degrees C
• -70 degrees C Ultracold freezer implies -60 to –100 degrees C Official policies regarding shipping conditions and long-term storage, are available here
Why are products recommended for storage in the freezer often sent out at room temperature?
In order to provide you with cost savings, items that are recommended for long terms storage in the fridge or freezer may well be sent out at ambient temperature if they are recognised from our product and transport history as being stable at ambient temperature in the short term (8-10 days). If you are concerned to receive a product on ice it is possible to request this through customer services but if this is not standard for the product there may be an additional 'ice' charge for the delivery. Our ‘Official Policy Statement on Shipping' is available here
My product has been kept at a temperature other than that recommended for storage. Will it be OK?
This really depends on the nature of the product.
Many products that we recommend for storage in the fridge or freezer will actually be delivered at ambient temperature, where we are confident that they are stable for at least 8-10 days under these conditions. We would advise that a product supplied on dry ice should not be used if it has been allowed to warm to ambient temperatures. Some products recommended for storage at 2-8 degrees will actually be OK for storage also at –20 degrees, others such as proteins or enzymes may be denatured or inactivated by freezing. Please contact Technical Services if you are unsure regarding the stability or storage of your product. Email: Technical Service
When a product is recommended to be stored under an inert gas, how do I do this?
Where products are recommended to be stored under an inert gas to prevent degradation of the product, rather than for safety considerations: Storing the product under nitrogen may be as simple as connecting a tube to a cylinder of nitrogen and holding the end of this tube emitting gas over the open bottle of chemical before tightly closing the lid. For handling and storing a product under nitrogen you might use a nitrogen-filled hood or perhaps an Atmosbag (example product Z530212).
Can you provide solution stability information for products?
Solution stability information will often be included in the Product Information, or Technical Datasheets for products. Where solution stability information is not available we would recommend preparing solutions fresh each time immediately before use. Some further testing may be needed to establish solution stability. We do not routinely test the stability of products in solution as part of quality control.
Where can I find the expiry date for a product?
The expiry date for a product will be indicated on the packaging in which the product is supplied, and will also be indicated on the Certificate of Analysis for the product. There are some exceptions in the range where the exact expiry date is only shown on the bottle. An expiry date is a final date after which the product should not be used. It is different from a retest date, where, if the product meets specification after re-assay, a new extended date may be assigned. Our ‘Official Product Dating Information Statement’, is available here
What is the shelf life for a product once opened?
The retest and expiry dates that we assign to products are for the unopened product, as supplied, stored appropriately. We cannot provide shelf lives for the opened product since subsequent handling and the application it is being used in will to some extent determine the useful lifespan of a product once opened. If handled carefully and stored appropriately the product could potentially be used up to the date assigned to the unopened product.
What is a retest date?
Products covered under the re-test program will have the QC Release Date and the Recommended Re-Test Date on the Certificate of Analysis. This date assigns the time frame during which the batch is expected to remain within established specifications, if stored under Sigma-Aldrich’s defined conditions. The Re-Test Period has been established by review of the product, or a comparable product’s history. The Recommended Re-Test Date for individual lots may be extended subject to quality review. If extended, a new QC Release Date and Recommended Re-Test Date will be published on the Certificate of Analysis.
The QC Release Date is the point in time when analytical data has been reviewed as confirming compliance with product description, specification and lot uniformity. Our ‘Official Policies Relating to Product Dating’ are available here
The label on the product says 1mg but there is much less than this in the bottle?
American formatting of numbers in the catalogue and on the labels of products can lead to some confusion. In America a zero is not normally written before the decimal point, thus ‘0.1’ is written as ‘.1’. If you believe you have received a shortfilled product please contact technical services and we will be happy to investigate further. Email: Technical Service.
Can I return my empty gas cylinder to Sigma-Aldrich for recycling?
There are a limited number of products where gas cylinders can be returned for reuse. Please contact our customer services team for more details. Email:
Can I request specific packaging for a catalogue product?
Pack sizes other than those listed in the catalogue, may be ordered as custom items through SAFC or our Custom Packaging Service depending on the quantities and the products you require. Please contact Technical Services if you are interested in a quotation. Email: Technical Service
How do I get material out of a drum?
We have various products available from the Labware range of products that might be used in opening or dispensing chemicals from drums. Information on drum equipment can be found here
Where can I find information on the various packaging formats that Aldrich products are supplied in?
You can find Aldrich Technical Bulletins, including those with information on the various Aldrich Packaging systems (Sure-Seal, Pur-Pac, UN-Pac, Versa-Flow etc.) here.
How can I find out what packaging a product will come in?
The packaging for a product will often be included in description for the product on our website. For more details or where packaging information is not clear please contact Technical Services. Email: Technical Service.
What information may be found generally on the labels for products?
Information shown on the labels for Sigma-Aldrich products is demonstrated through the link here
Where can I find out how to dissolve my product?
The solubility of many products is tested during quality control. Details of the method of testing and results can be found in the Specification for the product and on the Certificate of Analysis respectively.

The solvent that we use to test the solubility of a product may not be the best solvent for every application, but will generally suggest whether the product is likely to be more soluble in aqueous or organic solvents.

Additional information relating to the solubility of a product can often be found in Product Information Sheets and Technical Documents where available, and in the product listing, and description on our website.

Where solubility is not tested and information is not provided in any of the related documentation, we would suggest checking the Merck index to see if there might be more information here. Some testing of the solubility may be needed. More information on solubility can be found here
What is the ‘Shelf Life’ for my product?
We will not generally assign a ‘Shelf Life’ to a product but will assign ‘Retest’ or ‘Expiry’ dates. Retest or Expiry dates for products, where available, will be indicated on the Certificate of Analysis for a product and for Expiry dates on the bottle in which the product is supplied. Retest Date - When a product reaches its’ retest date, if we have material remaining it may be retested to check that it meets specification and a new retest date assigned. Expiry Date - Once the product reaches the expiry date it should be discarded, and no longer used. There are a number of products that are not formally assigned retest or expiry dates. Where a product is not assigned a retest or expiry date we would recommend that you might set an essentially arbitrary shelf life of 12 months from date of shipment and if you have material remaining at the end of this period contact us to check if we have any additional information to support continued use of the product. Our ‘Official Policy Statement regarding Product Dating’ can be found here
How long will my product be stable for once opened?
We do not state Shelf Lives, Retest or Expiry dates for products once they have been opened, since the useful lifespan of a product after opening will depend to some extent on subsequent handling. If handled carefully and stored appropriately after opening a product might be suitable for use up until the Retest or Expiry date indicated on the Certificate of Analysis for the lot in question. We will not determine this.
How can I get my product to dissolve in water?
For many applications it is desirable that chemicals should be in aqueous solution, but many chemicals are not very soluble in water. One strategy that can be used to facilitate getting chemical into aqueous solution is to initially dissolve the chemical in an organic solvent like DMSO or ethanol and then to dilute the chemical further in water or aqueous buffers, but this may not always work. An alternative strategy that can be used is to complex the chemical with cyclodextrins. Information on cyclodextrins can be found here.

  • General
  • Air Monitoring
  • Analytical Reagents, Solvents and Standards
  • Gas Chromatography
  • HPLC
  • General
  • Conditions
  • Application
  • Sample Preparation & Purification
  • Spectroscopy
  • Syringes
  • Titration
  • Vials & Accessories
What is included in Analytical?
Most people will think of Chemistry when thinking about analysis, however, Biological Analysis is also included. Both Analytical Chemistry and Biology can be qualitative or quantitative. Although each technique used is often very specialised and specific, analytical science itself has a broad scope and is found in almost all industries. Analysis in research and development is often used to determine the presence of compounds, both items of interest and impurities/contamination. Analysis can be due to legal requirements, quality control or for research basis.
How do I know which solvent to use for my analysis?
Analytical Science covers a large range of analytical techniques, therefore no particular grade of solvent will be suitable for every application.As a starting point our Online Solvent Centre has information on different grades available and links to further information, including links to grade comparison charts of common solvents, and a supplier cross-referencing chart.
Sigma Aldrich has a wide range of adsorbents for Thermal Desorption - where do I start when choosing one?
Supelco produces a comprehensive selection of adsorbent tubes – Carbotrap™ tubes – offering superior performance for trapping and thermally desorbing organic compounds. Selection of the proper adsorbent(s) is critical to achieving the best results for a thermal desorption application. An ideal adsorbent tube will trap and retain compounds of interest for the entire sampling period, then allow total analyte desorption without thermal decomposition. The rate of release should be as rapid as possible, to minimize analysis time and provide the most efficient separation. Stable adsorbents ensure the best detection limits by minimizing the possibility of breakdown products interfering with quantification.
Because no single adsorbent is capable of trapping and efficiently releasing all compounds, many Carbotrap™ thermal desorption tubes contain more than one adsorbent. Multiple beds of adsorbents enable you to analyze a wider range of compounds in a single sampling. In multi-bed adsorbent tubes, the adsorbents are arranged in order of increasing adsorbent strength, from sample inlet to sample outlet. The largest molecules in the sample are trapped by the first bed of adsorbent. Smaller molecules are trapped by the succeeding, stronger beds. To avoid forcing analytes through an adsorbent that is too strong, desorption flow is always in the direction opposite of sample collection flow. Choosing the correct sorbents for your application is a challenge. Using our adsorbent selection guide can help with this process.
I am interested in passive sampling - does Sigma-Aldrich have products for this?
  • Yes via out Radiello range of products. Passive or diffusive sampling relies on the unassisted molecular diffusion of gaseous agents (analytes) through a diffusive surface onto an adsorbent. Unlike active (pumped) sampling, passive samplers require no electricity (expensive pumps), have no moving parts, and are simple to use (no pump operation or calibration). After sampling, the adsorbed analytes are desorbed off the adsorbent by solvent or thermal desorption. Benefits of passive/diffusive sampling:
    • Compact, portable, unobtrusive, and inexpensive
    • Offers indication of average pollution levels over time periods of 8 hours to weeks/months
    • Requires no supervision, is noiseless and can be used in hazardous environments
    • Low cost allows for sampling at multiple locations (e.g., for highlighting pollution "hotspots"; or determining long term data trends in a specific geographical area)
    • Amenable to personal monitoring (breathing zone), indoor air analysis, and outdoor ambient air analysis
    Starter kits are available for the most common applications.  They provide a low cost 'taster' of this technology.
  • Are your Inorganic and Organic Standards produced in accordance with ISO EN 17025/ISO Guide 34?
    Yes and no!
    'Sigma Aldrich is committed to providing our customers with products that conform to the current EU legislation and UK accreditation body requirements.
    As a first milestone, our Swiss facility in Buchs has recently received double accreditation according to ISO/ IEN 17025 and also ISO Guide 34. All products produced under this double accreditation are established in the market as "TraceCERT" standards. For our organic standards products, there is an ongoing project to certify them according to ISO 17025 whereby qNMR, titration and HPLC will be added to the scope of accreditation soon.' In the meantime, we have datapacks available for the majority of our standards that give substantial information on how the standard was prepared.  Please check with your institutes UKAS auditor that this is acceptable.
    I need an Analytical Standard that is not in your catalogue. Can you help?
    Yes. Through our custom analytical service, we are able to provide non standard mixes for analytical testing purposes. A general rule of thumb is that if we have the chemical in our extensive portfolio, we can out it in a custom mix for you. Information we need to have;
  • What components – preferably with a CAS number
  • What level each component needs to be eg 1000ug/mL
  • What solvent is required to mix everything together eg methanol, dichloromethane etc
  • Do they need a certificate of analysis (either an HPLC or GC trace), gravimetric etc
  • What packaging and quantity do you want, e.g. 4 x 2mL vials, (custom possible)
  • Do they need separate ‘lots’ for QC and calibration purposes (aka Separate Source)
  • Please contact with your query.  Typical delivery for custom standards is 2-3 week, although this will depend on the analytes that are required.  There is a minimum quantity of 4 units, and a certificate of analysis is available upon request.
    Why do I have extraneous peaks / ghost peaks?
    Solvent Problems.
    Switch to a higher boiling solvent and make a run.   Does the extra peak still show up? Most often it will not. The customer needs to find a cleaner solvent for their analysis. Sigma-Aldrich provides a comprehensive solvent selection guide though our Grade Comparison Chart and Solvent Centre Another check of solvent contamination. With temperature programmed runs ask the customer to make a run with-out an injection. If it was a solvent problem you will not get a peak. Then have them inject the solvent with no compounds in it. Does the peak show up? If the answer is yes then the solvent is the cause. Contaminated Inlets
    Contaminated inlets are often a result of an injection size that is too large. This will cause some of the sample to back-up and contaminate the metal area and lines before the injection port liner. This area is not well swept and will allow residue to build-up.   Future injections will pick up some of this residue with each injection. The solution is to clean the entire injection mechanism and reduce the size of the injection. Other Causes
    1. Fat peak showing up early in the run - a heavier than normal compound is showing up in the sample. The peak seen is from the previous run. That is why it is wider than the other early eluting peaks.
    2. New peak is the same size peak as other early eluting peaks. We may have a new compound in the customers sample. Does the calibration sample show this same peak? If not the new peak may be real.
    How can I convert to Fast GC?
    Converting a conventional GC method to a Fast GC method is not as simple as just switching to a shorter column. It depends on how resolved the analytes are in the existing method. Instrument parameters (injection volume, split ratio, ramp rate, liner velocity, etc.) should be re-optimized when switching column dimensions. The following attachment includes both practical and theoretical discussions concerning Fast GC.

    For further details refer to our brochure ‘Fast GC’ T407096
    For our range of Fast GC Columns you can visit our column selection centre.
    Why do the ends of my glass columns chip and crack?
    The answer to this question lies in the installation of the glass column into the injector and detector ports.

    When installing a glass column, after gently sliding the column all the way up to the detector and injector stop positions, back the column down approximately 1/6” to 1/8”. This allows for expansion of the glass due to the elevated temperature of the injector and detector ports. If the column is not dropped slightly, the pressure from the expansion will cause the column to chip or crack.
    Why doesn't my Packed Column fit my GC?
    Many chromatographers follow methods cited in literature or manuals. Often a column is ordered as described in the method without considering the type of instrument the column is going to be used with.

    A classic example is the 3mm id glass column. A 5mm OD column has a 5mm OD, which is specific for Shimadzu instruments. A 3mm ID column will not fit a 1/4 or 1/8 injector or detector port. When placing an order for a packed column, confirm that the column being ordered will fit your instrument.

    Please contact Technical Servicee if you require a custom made packed GC column.
    Why doesn't my column fit my GC? It is too small or too large in OD.
    Many chromatographers follow methods cited in literature or manuals. Many times a column is ordered as described in the method without considering the type of instrument the column is going to be used in. A classic example is the 3mm id glass column. A 5mm OD column has a 5mm OD, which is specific for Shimadzu instruments.  A 3mm ID column will not fit a 1/4 or 1/8 injector or detector port. When placing an order for a packed column, confirm that the column being ordered will fit your instrument.
    I need a GC column, but the dimensions I require are not in your catalogue.Can you help?.
    Yes. Through our custom analytical service, we are able to provide a wide range of both packed and capillary columns of non standard dimensions. Information that is required; Capillary GC
    • Length (m)
    • ID (mm)
    • Phase type and thickness (um)
    • Instrument (some instruments require the column to be wound on a smaller cage)
    Packed GC
  • Column Length (m)
  • Material of the column ie, glass, teflon stainless steel etc.
  • I.D. (mm)
  • O.D. (mm)
  • GC name and model number (if model not known will require X = length of injector arm, Y = length of detector arm, S = span-injector to detector)
  • Packing material (mesh size and material plus treatments if needed)
  • Percentage loading of active phase (if required)
  • Preconditioned or not
  • Type of injection, (on column or off column)
  • Please contact with your query.  Typical delivery for a custom GC column is 2-3 weeks.
  • HELP! I have NO IDEA where to start in choosing a column for my application!
    Don't worry - this is a common issue, especially for more unusual analytes. We have a wide range of columns for both specialist applications and more routine analyses.  To help you decide which column will give you optimum performance, please download our GC column selection guide in our learning centre. This contains the information you will require, in very easy to use look up tables.  It is split up by application, or by market segment, so you can see at a glance which of our products would be most suitable. It also has information on how your analysis will be effected by changing dimensions and phase thickness. We also have a troubleshooting document that can help you to identify problems with your analysis and how to rectify them.  It is available to download in our learning centre as (link bulletin 853 - Capillary GC Troubleshooting Guide: How to Locate Problems and Solve Them.  You can also find a wide range of application literature here. Bulletin 853 - Capillary GC Troubleshooting Guide: How to Locate Problems and Solve Them.

    Please select a subtopic for HPLC on the left side

    When should I change my HPLC Guard Column?
    Considering the expense of HPLC Columns, the use of a guard column is an essential part of the analytical scheme. The difficulty is in knowing when to change the guard column. Waiting for a noticeable increase in pressure drop across the system may cause damage to the main analytical column. A dirty sample can foul a guard column very quickly and repeated sample introductions on to the same guard column can cause breakthrough of material from the guard column to the main analytical column. The best way to determine when to change the guard column is to observe the chromatography the system is producing. Monitor the peak symmetry of one compound in the sample when the system is new. Then periodically monitor that peak's symmetry throughout the course of the work. If any type of insoluble material is building up on the guard column, adsorption will occur and the peak will begin to tail slightly. Usually, the internal standard can be used as the peak to monitor because it is of known purity and concentration. Also, many data systems are available which can perform the peak symmetry measurement automatically
    Which HPLC fittings should I use?
    HPLC fittings are not always interchangeable. Nuts and ferrules are made specifically to fit a manufacturer's own products; consequently, variations often exist between fittings produced by different manufacturers. Some fittings cannot be interchanged because of variations in the shape of the ferrule and the seating depth of the tubing (the distance between the end of the 1/16" stainless steel tubing and the bottom of the ferrule). Waters, Valco@, and Rheodyne@ fittings, for example, cannot be interchanged. SUPELCOSIL™ HPLC columns require the use of Valco fittings (with 0.080" seating depth). The following is a sample of manufacturer seating depth specifications:

    Supelco 0.080"
    Waters 0.130"
    Upchurch 0.090"
    Parker 0.090"
    Swagelok 0.090"
    Valco 0.080"
    Rheodyne 0.170"

    If your HPLC fittings leak, determine whether they match the requirement for your column or instrumentation. When installing new ferrules and fittings on HPLC tubing, make sure that the tubing is at the proper stop position before you tighten the fitting. Once a fitting is tightened, the ferrule is seated permanently and cannot be used with other types of end fittings. This restriction can be avoided by using Fingertight, LiteTouch, EZ Grip, or Dynaseal fittings as long as they are compatible with the column, filter, or other component you are connecting to your system.
    What problems could I get with a mobile phase filter?
    Shifting retention in HPLC applications can be created by several phenomena.

    One of the most common sources is a clogged mobile phase filter (stone). To determine if the stone is a source of shifting retention times in a HPLC system, time the mobile phase flow rate with a cylinder and stopwatch. If the flow rate is correct, then a clogged filter is not the problem and other avenues need to be checked.

    If the flow rate is incorrect, remove the mobile phase filter and time the flow rate again. If the flow is correct, the filter needs to be replaced or sonicated in 50/50 methanol water and/or in 0.2% H3PO4/ACN (50:50). Rinse the stone with DH2O
    What can cause excessive backpressure?
    There can be many causes of excessive backpressure but one very common cause is build up of foreign materials on the top of the HPLC Column. This situation can be caused by sample precipitation (retains or accumulates) or dust and other particles from the degradation of the pump seals.

    This situation can be avoided by the use of a guard column. When you reach excessive backpressure, simply replace the guard column.
    What is a ballistic gradient?
    A ballistic gradient is a very fast separation technique used mostly in LC-MS applications. The complete analysis can take less than one minute and up to five. Non-optimal, high flow rates or linear velocity are combined with fast gradients and very short columns.
    What is dwell volume?
    Dwell volume is simply the time delay for a gradient change to reach the top of the HPLC column. It is important to remember that each HPLC system has its own dwell volume and this will affect the separation results. THIS IS A MAJOR REASON GRADIENT METHODS MAY NOT TRANSFER.

    Click here to view how to determine dwell volume.
    What determines the retention or hydrophobicity of a molecule in HPLC?
    Much of the retention of a column in Reverse Phase chromatography is due to what is commonly called hydrophobicity. This natural phenomenon is due mostly to the size of the hydrophobic (water resistant) area of a molecule. Retention will increase with the amount of water in the mobile phase. In general, the more hydrophobic the molecule (see Octanol/Water Partition Coefficient) the longer it should be retained.
    Why does the metal content of a silica particle contribute to the peak shape of my chromatogram?
    The electron withdrawing property of trace metals in silica particles enhances the negativity of surface silanol groups and contributes to peak tailing in silica with high levels of trace metals.
    Should I filter my HPLC solvents and buffers before use?
    The most common cause of excessive backpressure is due to the accumulation of particulates and permanently adsorbed materials at the top of the HPLC Column. This could be precipitated or un-dissolved particles that can come from your samples or your mobile phase.

    The best way to minimize accumulation on your column is to filter your samples, solvents and buffers with a .45µm or a 0.2µm syringe filter or through a filter flask before use. This should give you a longer column lifetime. Another way to minimize this build up is to use either an inline solvent/mobile phase filters, a guard column or a MicroSolv Column Saver. These disposable devices are low cost and easy to use without disrupting your chromatographic results.
    I heard that rapid changes in column backpressure can damage the column. Is this true?
    Yes, definitely.

    Exposure to rapid changes in back pressures in HPLC columns can cause a type of “pressure shock” and cause damage. Limit the pressure in your columns to 5,000 psi and avoid rapid changes such as manual injectors that “slam” the pressure. For this and other reasons, it is best to operate your HPLC system with pressure cut off around 3,500 psi. This will protect your columns from this damage.
    What special care should I take to protect my columns when I am equilibrating them?
    When you are equilibrating your columns for the first time or whenever changing your HPLC methods it is wise to consider not putting anything into the columns that can precipitate or is immiscible with the storage or current solvent in the column. Always ensure that the column is fully equilibrated with your mobile phase before making any injections.

    Depending on column type, this could range from 10 to 15 column bed for typical reverse phase to 50 to 100 bed volumes with polar embedded phases. Beware of buffers that might be in your column before you change the mobile phase composition with respect to the organic content. This can cause immediate precipitation and ruin your columns.
    What is a "system peak"?
    Both analytical and preparative liquid chromatography separations are often performed using mobile phases containing more than one component. When samples are dissolved in a different solvent than the mobile phase, after the injection an additional signal called the “system peaks” can appear.

    The presence of these peaks is explained through loss of equilibrium in the analytical or preparative column caused by competitive interactions between the separated solutes and the strong additive of the mobile phase. During the relaxation process the system peaks are being generated. It is worth noting that even if the system peaks are often misinterpreted they offer valuable information regarding the thermodynamics and kinetics of the separation, which takes place in the chromatographic system.

    However from the method development point of view system peaks should be avoided by dissolving the sample in a solvent that closely matches the mobile phase composition.
    I need an HPLC column, but the dimensions I require are not in your catalogue. Can you help?
    Yes. Through our custom analytical service, we are able to provide a wide range of analytical and preparative HPLC columns and guard columns of non-standard dimensions.

    Information that is required:
    • Column Length (mm)
    • Column I.D. (mm)
    • Phase packing

    Please contact Technical Service with your query. Typical delivery for a custom HPLC column is 4-6 weeks.
    What is an octanol/water partition coefficient?
    Basically, this is a measure of the hydrophobicity v hydrophilicity of a compound. It is extremely useful when combined with the pI of your molecule to predict retention times.

    The Octanol-Water Partition Coefficient is a physical property used to describe a chemical’s lipophilic or hydrophobic properties. It is the ratio of the concentration of your compound in the octanol phase to its concentration in the aqueous phase at equilibrium. It is commonly measured and labelled as Log P. Compounds with large non-polar structures usually have high Log P values and for compounds with highly polar groups, it is usually very low.
    What pH should I use for bonded silica columns?
    Operate silica and bonded silica columns within a pH range of 2.0 to 7.5 as a higher pH will dissolve the silica, creating voids in the column.

    Lower pH can eventually strip away some of the bonded phase. These defects will cause changes in retention times and loss of resolution.

    An apHera C18 column may be best if you need to work at extreme pH. apHera C18 columns are compatible with the commonly used reversed-phase HPLC eluents between pH 2 to pH 13: apHera™ Polymeric HPLC columns, high pH applications
    Will running a reverse phase silica analytical column in basic and then immediately in acidic conditions damage the column?
    Running an analytical column from one end of the pH spectrum to the other should not be an issue as long as the maximum and minimum pHs are not exceeded.

    All that will occur is an acid/base reaction in the column creating a salt and water. The only exceptions to this rule would be if the reaction was extremely exothermic, or if the produced salt is insoluble in your mobile phase. Insoluble salt in the mobile phase is not a column killer, but it will temporarily increase backpressure and reduce column efficiency until it can be removed (typically by flushing the column thoroughly with warm deionised water).

    If the salt created is insoluble in all of your subsequent wash steps this can be more of an issue. Certain salts will be insoluble in most solvents (even water) unless it is pH adjusted. Flushing the column with a pH 8 deionised water may help to remove such contamination from the column, which other steps may not have touched. Following this step with a 100% deionised water wash to remove the basic component from the column prior to re-equilibrating in mobile phase might be a good idea. At this point the column will not be damaged any further by a higher pH wash step, so it might be worth a try to see if it will help restore performance. Raising the temperature in the column could inflict more permanent damage to the column, if it breached the maximum temperature of the column (60 degrees C) for an extended period, but it is unlikely that this will happen.
    What solvents can be used with silica-based reversed phase columns?
    Silica-based reversed phase columns can be used with all common HPLC grade organic solvents. Buffers made from acetate, citrate, formate, and phosphate salts at concentrations up to 0.2M have been used without adverse effect. Organic modifiers and ion pair reagents also present no problems as long as the appropriate pH range is not exceeded.

    Because ion pair reagents are often difficult to completely flush from the column, columns used with these reagents should be dedicated to the particular analysis involved. Limit the use of strong acids and bases to amounts needed to adjust the pH of the mobile phase. Be careful not to mix, or use in sequence, solutions that might precipitate or gel in the column or system.
    What pressure can be used with HPLC columns?
    Silica-based HPLC columns can operate at pressures up to 4000psi, except for anything over 4.6mm ID, then operate at pressures less than 3000psi. Resin-based columns are limited to much lower pressures. You can expect a gradual increase in backpressure as the column ages. A sudden increase in pressure usually means that there is a plugged/blocked frit at the column inlet. To unplug/unblock the frit, reverse the column and flush with an appropriate solvent, with the column disconnected from the detector.
    What temperature can be used with silica-based HPC columns?
    Supelco silica-based columns have been used successfully at temperatures up to 75°C. However prolonged use at temperatures above 75°C can shorten column life. Refer to your column specification sheet for further details.
    Why do some methods use low pH buffers to separate acidic compounds?
    By suppressing their ionisation at low pH, acids will be more like neutral compounds and will retain on HPLC columns much the same way that neutral compounds would.

    Another benefit of running on Type A and Type B silica at low pH is that the silanol activity is reduced. This should sharpen your peaks.
    What are the typical flow rates recommended by HPLC column companies to start with, for various column ID’s?
    Although it will vary from column manufacturer to column manufacturer, and is very dependant on the column length back pressure the following is good rule of thumb for common columns.

    Column Dimensions Recommended Flow Rate
    1.0 30-60µL/min
    2.1 0.1-0.6mL/min
    3.0 0.3-1.5mL/min
    4.6 0.8-3.0ml/min
    7.8 4.0-10mL/min
    How can I increase the lifetime of my HPLC Column?
    To get the most lifetime from your analytical column, ensure you clean up your sample before injecting. Always use a guard column and flush your analytical column on a regular basis. Doing the right things from the beginning can save both time and money in the long run.
    What is “aqueous-normal phase” chromatography?
    In aqueous-normal phase, the maximum retention time of analysed compounds is obtained with 100% acetonitrile (least polar solvent) as the mobile phase and as you increase the polar solvent content (aqueous), retention is decreased.
    When should I use an amino HPLC column?
    Amino columns are used mainly in Normal Phase HPLC for separation of polar compounds which are difficult to retain and separate by RP-HPLC. The main classes of compounds that are separated using amino HPLC columns are: oligosaccharides, glycoalkaloids, surfactants, polar pharmaceuticals and impurities, tocopherols.

    Cogent Type C columns can be used to separate the above compounds in Aqueous Normal Phase mode using acetonitrile / DI water mobile phases.
    What are the advantages of using a 3.0mm ID HPLC column for LCMS?
    Many scientists use a 2.1mm ID and smaller columns for LCMS which have optimal flow rates of approximately 0.3ml/min.

    This is fine for isocratic analysis but when you use a gradient method, specialised pumps and mixing valves are necessary that can reproduce the very small changes in the mobile phase’s composition. 3.0mm ID columns use more traditional flow rates and can be used easily on LCMS without specialised pumps for both gradient and isocratic methods.

    Also, when using small column ID’s it is important that you invest the time to completely optimise your system’s plumbing to minimize extra-column band broadening and achieve acceptable chromatography. If you have sufficient sample for loading, you may want to consider using a 3.0mm ID column for any situation that a 2.1mm ID has been recommended.
    What lifetime should I expect from a Cyano HPLC column?
    While Cyano HPLC columns have suffered from a reputation of not lasting very long, with type B silica (high purity) and proper bonding technologies, a Cyano column that is conditioned and treated properly should last as long as any other column. To lengthen column life avoid using mobile phases with a pH higher than 7.0 with Cyano and Amino columns.
    I am confused when it comes time to use Phenyl, Amino or Cyano columns. What are the main differences?
    All these columns will offer different selectivities in reverse phase compared to a C18 or C8 column.

    Amino, and Cyano columns can be used as both normal and reverse phase. It is best to dedicate a particular column for either reverse or normal phase and not to change back and forth.

    Phenyl columns are more robust and rugged than cyano and amino but normally used only in reverse phase separations. Phenyl columns like C18 or C8 tend to retain samples based on hydrophobicity.

    A mixed interaction involving hydrogen bonding and dipolar interactions are responsible for the retention of solutes on cyano-silica columns and weak hydrogen bonding interaction leads to separation on amino-silica columns.
    What is the first step that you would recommend in developing a new HPLC method and where should I start?
    An easy way to start any HPLC method development is to look in the USP, BP or other reference sources. If you cannot find a similar method to modify, contact one of the HPLC column manufacturers. Often their technical support can be very helpful and at no cost.
    What performance standards should I set for a routine method? How do I go about developing this?
    You should define your goals as loosely as possible then determine resolution, tailing, precision, LOQ and linearity goals. Also include such important factors as maximum analysis time, sample prep complexity factors and cost. You may want to also develop your methods to be LCMS compatible.
    I am analysing Metformin in plasma samples using Acetonitrile + Deionised Water with 0.5% Formic Acid. How I can obtain reproducible results and peak shape?
    You can try substitute formic acid in deinoised water by adding ammonium acetate (10mM) and acetic acid (1%) to the aqueous phase. This should improve the reproducibility of peak areas and retention times. In addition extensive reconditioning of the analytical column with pure acetonitrile in between separations is essential for good reproducibility when working with plasma samples.
    My chromatography isn't what I expected - what have I done wrong?
    C18 columns have become the industry standard and are selected for HPLC methods most of the time. Dispersive interaction forces are sufficient to allow C18 columns to retain and separate many organic compounds; however, results are not optimum in all cases.

    There is certainly nothing wrong in starting with a C18, but our experience has shown that selectivity, retention and efficiency can all suffer with certain samples. Poor or marginal results can occur up to 50% of the time depending on sample type. Modern polar phases are highly complementary to alkyl phases and may produce much better results for these compounds. C18 columns are becoming much alike due to evolution of silica particles and development of improved bonding chemistry. Changing from one brand of C18 to another may not produce a different, better result. When resolution is not acceptable for any reason, an alternate stationary phase with more polarity than C18 or C8 may be the best answer.

    Polar stationary phases such as Ascentis Phenyl and RP-Amide can play a unique and important role in changing retention and selectivity for certain classes of compounds. We have a wide range of instructional videos to help with method development, and they also give hints and tips on how to solve the following chromatographic problems:

    • Poor selectivity
    • Peaks overlap or elute in wrong order for best quantitation
    • Poor retention
    • No retention; sample elutes at column void volume v
    • Unstable separation; phase not wetted by high aqueous mobile phase causing loss of efficiency and retention
    • Poor peak shape (low efficiency)
    • Too much retention and selectivity (requires gradient)

    They can be found in the video section of our learning centre 
    What is the difference between SPME and SPE?
    SPME - Solid Phase MicroExtraction is an innovative, solvent free technology that is fast, economical, and versatile. SPME is a fibre coated with a liquid (polymer), a solid (sorbent), or a combination of both. The fibre coating removes the compounds from your sample by absorption in the case of liquid coatings or adsorbtion in the case of solid coatings. The SPME fibre is then inserted directly into the Gas Chromatograph for desorption and analysis. SPME has gained wide spread acceptance as the technique of preference for many applications including flavours and fragrances, forensics and toxicology, environmental and biological matrices, and product testing to name a few.

    SPE - Solid Phase Extraction is a technique designed for rapid, selective sample preparation and purification prior to chromatographic analysis. Using liquid chromatography principles to control selectivity, SPE provides the sample clean up, recovery, and concentration necessary for accurate quantitative analysis. The multitude of available phase chemistries can be packed into an array of hardware formats such as glass tubes, 96-well plates, preparative SPE Büchner funnels and dispersive SPE, and can be processed using dedicated vacuum manifold accessories.

    Essentially, SPME is used for volatile chemical analysis - usually in conjunction with GC.

    SPE is used for non-volatile analysis - usually with HPLC, but can be used for preparing samples for GC.
    How do I choose the correct SPE phase?
    SPE can be thought of as having similar selectivity as HPLC - so most people start with C18. However, C18 might not be the best phase to remove the sample interference.

    Using the flow chart in our learning centre and looking at the principles of method development can significantly reduce the amount of time required to troubleshoot your method, and give you cleaner extracts for superior chromatography.
    How do I use SPME?
    This is a common question, and in response, we have developed a number of instructional videos. These are available from our learning centre In addition, an on-site demonstration may be booked through your local analytical representative, or via
    What SPME fiber should I use to extract a class of analytes?
    Two factors should be considered when selecting the correct fiber:

    • Polarity of the analytse
    • Volatility and molecular size of the analytes
    Polar analytes are attracted to polar phases (e.g., polyacrylate and Carbowax coatings). Fibers with a thicker film (100µm) are better for volatiles, but also can be used for less volatile compounds (longer extraction times are required). Porous fibers (with Carboxen or divinylbenzene coating) also can retain small analytes, and are ideal for C2-C6 analytes Thinner film fibers (7µm and 30µm polydimethylsiloxane) are better for larger molecules.
    How can I improve SPME recovery?
    To improve the recovery using SPME you should follow these steps:

    • Select the most appropriate.
    • Agitate or stir the sample.
    • If you are performing headspace sampling, minimize the headspace volume (<30%) Select the appropriate temperature (40-90°C). Analytes can desorb from the fiber if the temperature is too high.
    • Add 25% NaCl to the sample and adjust the pH (reduce the pH for acids, increase the pH for bases).
    • Minimise the amount of organic solvent in the sample.
    Is SPME quantitative?
    Yes. A calibration curve to determine linear range is required for each analyte.

    Using internal standards with properties similar to those of the analytes in the sample improves precision. Use of Standard Additions is best suited for complex matrices. For gas chromatography/mass spectrometry analysis, isotopes are ideal as internal standards. Consistent extraction conditions and stirring or agitation is required.
    How can I extend SPME fiber life?
    Most fiber damage is the result of needle bending. Bending usually occurs while the fiber is piercing the vial septa. Adjust the black needle depth gauge so that only 0.5-1cm of the needle is exposed. Pierce the vial septa, then screw the needle into the vial by rotating the needle depth gauge.

    Maintain the injection port temperature below the maximum recommended temperature of the fiber. Conduct headspace sampling whenever possible to minimize extraction or carry over of high molecular weight compounds that coat the fiber.
    My background is too noisy. How can I reduce extraneous peaks?
    • Ensure proper conditioning of the fiber before using it.
    • Reconditioning the fiber for a longer time.
    • Check the inlet liners. Most peak noise is caused by septa particles in the liner.
    • Change the vial septa.
    • Reduce the inlet temperature by about 20°C. Use the lowest temperature that produces sharp peaks and minimizes carryover.
    Can analytes be extracted from organic solvent using SPME?
    We do not recommend extraction from organic solvents. However, you may extract analytes using the headspace above polar organic solvents, at the risk of a reduced distribution constant, fiber damage from swelling, and a large solvent peak on your chromatogram.
    What is spectroscopy used for in analytical?
    Spectroscopy can be used qualitatively, quantitatively and for identification.

    Although often less obvious in modern laboratories, the spectrometry group of techniques is still the largest single most important group in analytical chemistry. The most common detectors used in techniques such as HPLC and GC will be spectrometric techniques, as well as the use of spectrometry independently for identification and qualitative analysis.

    The key principle in spectrometry is compounds having unique spectra produced from their energy changes in relation to the absorption or emission of radiation. Different techniques promote and detect different forms of radiation, but the basic principle remains the same.
    Does Sigma have spectroscopy specific products?
    Yes. For details of our products specific to your technique of interest please see our Spectroscopy pages.

    Or for technique specific solvents please visit our Solvent Centre.
    What is the accuracy of a Hamilton Syringe?
    Hamilton syringes are manufactured to be accurate within ±1% of nominal volume, and with precision within 1%, measured at 80% of total scale volume. The design of the barrel and plunger dimensions assures high levels of accuracy and precision. The Hamilton Company Quality System is ISO 9001-2000 certified.

    View the complete range of Hamilton Syringes available from Sigma-Aldrich.
    Is the volume of fluid in the needle part of the total volume of the dispensed fluid?
    When using a Hamilton syringe, the volume in the needle (called dead volume) is considered constant and the volume being dispensed is absolute. The dead volume is maintained throughout aspiration and dispensation stages.
    Are the plungers for the 700 series MICROLITER syringes interchangeable?
    No, they are not. Each plunger is fitted to a specific syringe barrel. Be very careful to keep each plunger with its original syringe in order to maximize syringe performance. 3
    What are the most versatile syringes made by Hamilton?
    GASTIGHT syringes are the most versatile syringes. The plunger is replaceable. Any of the Metal hub, Kel-F or Removable Needle allow for the replacement of needle if they become bent or plugged.

    View the complete range of Hamilton Syringes available from Sigma-Aldrich.
    How do I select the correct needle?
    You will need to answer the following questions:

    • What is your application and what instrument are you using?
    • Do you already have a syringe, and if so what kind? What is the volume and what is the termination?
    • What gauge do you think you need? Hamilton makes needles from 10-33 gauges.
    • What length do you need? The most common length is 2 inches (51 mm).

    Visit our Syringe Selection Centre for details of the complete range of syringes available from Sigma-Aldrich.
    Is a digital syringe automated or manual?
    The digital syringe is a manual syringe with a digital display that allows you to clearly see the aspirated volume.

    The digital syringe is not automated, it will not dispense with the touch of a button. It operates like a typical syringe, but there is no guessing as to the volume being aspirated or dispensed.
    What does “s” mean in 22s or 26s gauge needle?
    The “s” represents a smaller inner diameter for the needle and a thicker needle wall for better durability.

    For example, a 26 gauge needle has an outer diameter of 0.46 mm and an inner diameter of 0.26 mm while the 26s gauge needle has an outer diameter of 0.47mm and an inner diameter of 0.13mm. The 26s has half the inner diameter of the 26 gauge needle. The difference in the wall thickness is also nearly doubled with 26s gauge having a thickness of 0.18mm while the 26 gauge is only 0.10 mm.
    What is Titration used for?
    Titration is used to determine the concentration of a known reactant. Typical reactants are acidic and basic impurities, complexometric reactants or more specific reactants such as water.
    What is Karl Fischer Titration?
    Karl Fischer Titration is a technique for the determination of water content in liquids and solids. The principle has remained the same since it was first published by Karl Fischer in 1935. Key advantages of Karl Fischer over other moisture determination techniques include:

    • Selectivity for water
    • High accuracy and precision
    • Easy sample preparation
    • Suitability for analysing gases, solids and liqui
    Which vials are compatible with my instrument?
    When choosing Vials, the autosampler compatibility is obviously an important factor. For this reason, Supelco vials can be viewed divided by Autosampler, and are also available divided in the Autosampler section of our Vials Brochure.

    Vials can also be classified by the type of cap (crimp top, snap top, screw thread), the bottom (flat, rounded, round, conical), and the glass (clear, amber and silanised).
    Which caps are compatible with my vials?
    Once you have selected a suitable vial, you will most likely require compatible caps.

    If you have found your vials using the brochure, then suitable caps may be listed here: Vials Brochure (please confirm all specified details are suitable).

    Details to note are:
    • Type (screw cap, crimp top or snap top)
    • Vial diameter (eg. O.D. x H 15 mm x 45 mm)
    • Thread size (eg thread 8-425. (8 = outer diameter, 425 = height)
    • Maximum Operating temperature – Polypropylene 135°C, phenolic hole caps 149°C and phenolic caps 205°C.
    • Crimp cap opening
    Which Septa should I use?
    Vial septa are available in various materials, sizes, thickness, colours and pre-cuts.

    The first step is to determine the material by using the septa selection guide on page 6 of our vials brochure. This gives details of septa materials, their solvent compatibility, re-sealability and temperature limit.

    Next, consider the size of the septa. The size will be dependent on the size of vial, cap and opening.

    The thickness and pre-cut will be more personal/instrument preference, depending on the application, and as a fix to any previous problems. Colour, again, is personal preference, often used to easily distinguish samples.
    The Vials I need aren’t available in your brochure. What can I do?
    We are able to offer custom vial services, including silanization of vials, or custom ordering vials with specific dimensions.
    For further enquiry contact

    • General
    • Calculations
    • Material Science
    • Chemical Synthesis
    • Stable Isotopes
    • Solvents
    • Chemical Services / Drug Discovery
    I need a particular chemical but I can’t find it in your catalogue, can you help?
    You can search the Sigma-Aldrich catalogue in a number of ways including product name, CAS number, molecular formula and chemical structure (see below for the link to the Substructure Search tool). The most convenient way to search is to use the CAS (chemical abstract service registry) number, which is a unique identify number for a chemical. Use of the CAS number overcomes the potential for variation in the nomenclature used in naming chemicals. If you do not have the CAS number it can usually be found using a search engine on the Internet and typing in the ‘chemical name and CAS’ as a search term. The links to our structural search tool and the associated help on using this are below: The Substructure Search tool:
    Substructure Search Tool Help:
    A guide to searching on our website is also available here
    If no product matches are found when searching our website using the CAS number, this indicates that we do not have the chemical of interest available to offer as a catalogue product. If we do not have a chemical available as a catalogue product we may be able to source this product for you. Information on our chemical sourcing service can be found here
    Alternatively you might be able to identify alternative suppliers on a website like
    Where can I find information about the numbering of rings in chemical structures?
    Information on the numbering of rings in chemical structures can be found in the following links: Multiple ring numbering
    Heterocyclic ring numbering
    How do I dissolve my product?
    Sigma-Aldrich often includes a test for the solubility of a product, in a defined solvent and at a stated concentration, as part of the specification for its products. The method of testing and the actual result recorded in quality control will be shown on the Certificate of Analysis. If we do not test the solubility of a particular product then information may be available from other sources such as the Merck index. Further information regarding solubility can be found here
    What are the likely impurities in my product?
    The Certificate of Analysis for a product and a particular lot will show what testing is performed in quality control and what impurities are present. Unless there is testing for specific impurities included in the Specification for a product we will not, generally, have any information on what impurities are present. Levels of any impurities that we do not test for, may vary from batch to batch.
    I have an old bottle of chemical on the shelf is it still OK to use?
    The Certificate of Analysis will provide information about any expiry or re-test date that has been assigned to a particular product and batch. You will need the product code and the lot number to access this information. The Certificate of Analysis will either indicate that the product has got an Expiry Date or a Retest Date. In the absence of either of these dates on the Certificate of Analysis, it can be assumed that the product is not formally assigned a Retest or Expiry Date. For more information about these options please see our Dating Policy document, here
    What is Mesh size?
    A number of our powder products have a specified Mesh size. This is a measurement of the particle size determined using a sieve. "+" before the sieve mesh indicates the particles are retained by the sieve;
    "-" before the sieve mesh indicates the particles pass through the sieve;
    typically 90% or more of the particles will lie within the indicated range. A table indicating conversions from mesh size to micrometers can be found here.
    Can I get a Certificate of Analysis for a Rare Chemical Library product?
    Our Rare Chemicals are not supplied with Certificates of Analysis. This is due to the nature and origin of these products. Please see here for more information about this product range.
    Why has my DMSO arrived as a solid?
    DMSO has the property of supercooling easily. This means that it can stay solid above its melting point (16-19°C) especially if it is left standing in storage. It will melt very slowly at room temperature or can be re-liquefied by warming to room temperature (using a warm water bath) without detriment to the product.
    I have the structure for a chemical how do I identify if you have a product?
    You can search for a chemical with a known structure, using the Substructure Search tool, on our website.
  • The substructure search tool can be found here
  • Help on using this tool is available here.
  • A general guide to searching on our website is available here
  • How do I calculate the Normality of an acid or base from its Molarity?
    Normality can only be calculated when we deal with reactions, because Normality is a function of equivalents. Normality refers to compounds that have multiple chemical functionalities, such as sulfuric acid, H2SO4. A 1M solution of H2SO4 will contain only one mole of H2SO4 in 1 litre of solution, but if the solution is titrated with a base, it will be shown to contain two moles of acid. This is because a single molecule of H2SO4 contains two acidic protons (H+ Ions). Thus, a 1M solution of H2SO4 will be 2N. The 'Normality' of a solution is the 'Molarity' multiplied by the number of equivalents per mole.
    How can the Molarity of a percentage solution be calculated?
    Using 70% concentrated Nitric Acid as an example: 70% Nitric Acid means that 100 grams of this acid contains 70 grams of HNO3. The concentration is expressed at 70% wt./wt. or 70 wt. % HNO3. Some analysts prefer to work in acid concentration units of Molarity (moles/litre). To calculate the Molarity of a 70 wt. % Nitric Acid the number of moles of HNO3 present in 1 litre of acid needs to be calculated. Knowing the density of the acid, we can calculate the weight of 1L of 70% HNO3 to be 1400 grams. Knowing that the solution is 70 wt % would then allow the number of grams of HNO3 to be calculated: (0.700)(1400g) = 980.0 grams HNO3 per litre. Dividing the grams of HNO3 by the molecular weight of HNO3 (63.03 g/mole) gives the number of moles of HNO3 / L or Molarity which is 15.5 M. This theory explains the following equation used for calculating the Molarity of acids where the concentration of the acid is given in wt %: [(% x d) / MW] x 10 = Molarity; Where: % = Weight % of the acid;
    d = Density of acid (specific gravity can be used if a density value is not available); MW = Molecular weight of acid. Using the above equation to calculate the Molarity of the 70 wt % nitric acid: [(70 x 1.4) / 63.03] x 10 = 15.5 M
    What do the different notations Mw, Mn, Mv etc. used for the molecular weights for polymers indicate?
    The %ee (enantiomeric excess) of a product is often required when one isomer is more predominant than another isomer. The enantiomeric excess is a value which accounts for this. For an example, a product that is 75% R-isomer and 25% S-isomer has (75-25=50) a 50% excess of the R-isomer. %ee is commonly not directly tested for but can be calculated using the optical rotation. Example; Product 454486 is the R-isomer of 2,2-dimethyl-1,3-dioxolane-4-carboxaldehyde.  This product has an optical rotation [a]20D of +53.80 degree. The ee% is varying from lot to lot. For example lot 07028LC has a GC purity of 95.1%, with an optical rotation of +46.40degree. The general equation to use is:
    ( [a]20D of lot / [a]20D of Product) x 100% = %ee  For lot 07028LC:
    (46.4 / 53.8) x 100% = 86.2%ee.  The remaining 13.8% is evenly split between the R and S isomer giving 6.9% each.  This means that the total %ee of the R-isomer is (86.2+6.9) = 93.1%
    Because the lot purity is 95.1% the %ee of lot 07028LC will therefore be: 93.1 x 0.951 = 88.5%. 
    How does polarity influence choosing the correct solvent?
    The polarity of a solvent will determine what type of compounds it is able to dissolve and with what other solvent it is miscible. In a broader sense, solvents can be classified as "polar" and "non-polar". Non-polar reactants will dissolve in non-polar solvents while polar reactants will dissolve in polar solvents. There are three measures of the polarity of a solvent: Dipole moment, Dielectric constant & Miscibility with water. Solvents with a large dipole moments and high dielectric constants are considered polar. Those with low dipole moments and small dielectric constants are classified as non-polar. Solvents that are miscible with water are polar, while those that are not are non-polar.
    What do the different notations Mw, Mn, Mv etc. used for the molecular weights for polymers indicate?
    Unlike small molecules polymers are commonly made up of a mixture of varying sized molecules, with a wide range of molecular weights. As a result with long chain polymers it is normally only possible to determine the average molecular weight. There are several different methods for determining the molecular weight of a polymer. 1. Mn - Number-average molecular weight; is determined by measuring the molecular weight of n polymer molecules, summing the weights, and dividing by n.
    2. Mw - Weight-average molecular weight; Weighted average of polymers. Always larger than Mn. Mw is used as a squared function to calculate the value.
    3. Mz - Average molecular weight; Is measured by sedimentation analysis
    4. Mv - Viscosity-average molecular weight; Average determined by viscosity measurements. Closer to Mn than Mw
    5. Mp - GPC(SEC)peak molecular weight; Gel Permeation Chromatography (Size Exclusion Chromatography) Values given relative to a standard. Average weight relative to the peaks on chromatography trace.
    What is the particle size distribution of a product?
    The particle size distribution of a powder is a list of values that defines the relative amounts of particles present sorted according to size.

    We will generally only have information in particle size distribution for a product if it is included as part of the specification for the product.
    How do I remove an inhibitor that is present in my product?
    Some monomers are supplied with inhibitors such as 4-tert-butylcatechol (TBC) or 4-methoxyphenol (MEHQ). These inhibitors need to be removed for polymerisation to take place. Sigma Aldrich has a range of prepacked columns that can be used for inhibitor removal.

    A link to a list of inhibitor removal column products can be found here
    How do I calculate the enantiomeric excess of an isomer?
    The %ee (enantiomeric excess) of a product is often required when one isomer is more predominant than another isomer. The enantiomeric excess is a value which accounts for this.

    For an example, a product that is 75% R-isomer and 25% S-isomer has (75-25=50) a 50% excess of the R-isomer.

    %ee is commonly not directly tested for but can be calculated using the optical rotation.

    Example; Product 454486 is the R-isomer of 2,2-dimethyl-1,3-dioxolane-4-carboxaldehyde.

    This product has an optical rotation [a]20D of +53.80 degree.
    The ee% is varying from lot to lot.

    For example lot 07028LC has a GC purity of 95.1%, with an optical rotation of +46.40degree.

    The general equation to use is:
    ( [a]20D of lot / [a]20D of Product) x 100% = %ee

    For lot 07028LC:
    (46.4 / 53.8) x 100% = 86.2%ee.

    The remaining 13.8% is evenly split between the R and S isomer giving 6.9% each.

    This means that the total %ee of the R-isomer is (86.2+6.9) = 93.1%
    Because the lot purity is 95.1% the %ee of lot 07028LC will therefore be: 93.1 x 0.951 = 88.5%.
    Where can I find a list of chiral building blocks and catalyst for Asymmetric Synthesis?
    Sigma Aldrich offers a market-leading range of innovative chiral catalysts and ligands, chiral reagent, chiral auxiliaries, chiral building blocks and chiral resolution reagents for asymmetric synthesis.

    A list of these is available here: Asymmetric Synthesis
    Where can I find a list of Aldrich Technical Bulletins?
    The Aldrich technical bulletins can be found here: Technical Bulletins
    How do I find a chemical labeled with stable isotopes on the Sigma-Aldrich website?
    To find a labelled product on our website use the name of the chemical without any mention of labels (e.g. do not include 13C or D). Available labelled products will be listed in the matches for this search. For example if you search for 1,1,2,2-tetrachloroethane, amongst the matches you can find 1,1,2,2-tetrachloroethane-13C2 and 1,1,2,2-tetrachloroethane-d2.
    How do I find a chemical labeled with Stable Isotopes on the Sigma-Aldrich website?
    To find a labelled product on our website use the name of the chemical without any mention of labels (e.g. do not include 13C or D). Available labelled products will be listed in the matches for this search. For example if you search for 1,1,2,2-tetrachloroethane, amongst the matches you can find 1,1,2,2-tetrachloroethane-13C2 and 1,1,2,2-tetrachloroethane-d2.
    How to get price and availability information?
    The most common products will have price and availability details on our website.
    For products that do not show this information please contact our Technical Services with the amount of product you are interested in. Email Technical Service
    Can I order custom labelled products?
    If a particular labelled product of interest to you is not available on our website contact our Technical Services and we will check whether this product can be sourced for you. Email Technical Service.
    How do I get specific lot information or a Certificate of Analysis for a solvent?
    A Certificate of Analysis is available by lot for each of our solvents and can be accessed through our Advanced Search Option.
    Online Certificate of Analysis
    Who do I contact about larger solvent volume needs?
    Email us at or visit SAFC for development and manufacturing-scale inquiries.
    How do I know what packaging options are available for a solvent?
    The Solvent Centre gives you the ability to review all the specifications associated with our solvent packaging. This includes physical dimensions, closure types, dispensing methods, UN/DOT Rating as well as solvent compatibility: Solvent Centre
    Who do I contact if I need a solvent blend, which you do not carry?
  • Email us at For a complete listing of all our Solvent blends, visit the Solvent Center .
  • The dispensing of solvents provides some challenges due to the number of container options available. What dispensing options are available for each container?
    The Sigma-Aldrich Solvent Center provides numerous dispensing options for each container type.
    Why on occasion does my Methanol have an unusual odour? Does it affect the product purity or performance?
    Industry research has indicated that unusual odors in methanol are a common problem and stem from low - level mercaptans and / or amines found in the natural gas raw materials used in production. Odors from these types of compounds can be noticeable at low part per million (ppm) levels and have not been shown to have any negative impact on product performance at these concentrations.
    GC Analysis of Methanol with Off - Odors
    What are some of the preservatives used in the most common ethers and chlorinated solvents and why are they added?
    Certain solvents will degrade over time requiring special handling and storage considerations. In addition, the products of certain degradation processes pose a potential safety risk if present at sufficiently high levels. For these types of materials, small amounts of stabilizing chemicals are added to slow down or stop material degradation.
    It is important to understand the stability of materials in use and if unclear, consult the Sigma-Aldrich Technical Support and SDS Centers. Summary of Stabilizer Systems
    Why do peroxides form in certain solvents and how do I test for them?
    A significant number of laboratory solvents can undergo autoxidation under normal storage conditions to form unstable and potentially dangerous peroxide by-products. Molecular structure is the primary factor relating to a material’s potential for hazardous peroxide formation. It is important to understand the stability of materials in use and if unclear, consult Sigma-Aldrich Technical Support. Peroxide–Forming Solvents
    What is 190 proof and 200 proof ethanol?
    All ethanol products have a proof associated with the product description. The proof is a measure of the water content of the ethanol portion of the product. The proof is calculated as two times (2 x) the actual ethanol concentration by volume.
    Sigma-Aldrich Tax-Paid Ethanol Listings.
    What is solvent polarity?
    The polarity of a solvent will determine what type of compounds it is able to dissolve and with what other solvent it is miscible. In a broader sense, solvents can be classified as "polar" and "non-polar". Non-polar reactants will dissolve in non-polar solvents while polar reactants will dissolve in polar solvents. There are three measures of the polarity of a solvent: Dipole moment, Dielectric constant & Miscibility with water. Solvents with a large dipole moments and high dielectric constants are considered polar. Those with low dipole moments and small dielectric constants are classified as non-polar. Solvents that are miscible with water are polar, while those that are not are non-polar.
    Why do some solvents arrive as a solid?
    Melting points vary from solvent to solvent, so regional temperatures will affect the state in which a solvent arrives.
    How has the isomer composition of Hexane changed?
    Due to market wide shift, the isomer composition has changed from 85% n-hexane to 60-65%. This affects only our line of Hexane, Mixture of Isomers and does not apply to all of our solvents, which have an n-hexane content of 95% or greater.
    Can you explain the different concentration units used with solvents?
    A number of different unit of concentrations are often used to equate levels of water or amount of stabilizer in a solvent.
    Parts per Million (PPM) - 1 part in 1,000,000. 1 ppm is equal to 1mg/liter and 0.0001% by concentration.
    Parts per Billion (PPB) - 1 part in 1,000,000,000. 1 ppb is equal to 0.0000001% by concentration.
    Which solvent grade should I be using for my application?
    Sigma-Aldrich Solvent Applications Table gives a guideline to common applications and the appropriate solvent grades.
    What are the options for drying solvents?
    High-purity solvents with extremely low water levels specifically manufactured for moisture sensitive Organic and Biotech applications are available from Sigma-Aldrich. Sigma-Aldrich also carries various drying agents compatible with organic solvents. Related Information links are shown below:
    Which Aldrich Condenser should I use for a low-boiling solvent?
    The Sigma-Aldrich Glass Center incorporates a Condenser Selection Guide in its Technical Library to aid with the condenser selection process.
    What apparatus do you recommend for HPLC solvent filtration?
    The Sigma-Aldrich Vacuum Filtration Assembly gives you all the components you need including: funnel top, fritted glass funnel support, filtration flask, aluminum clamp, and silicone stopper. The Acrodisc Syring Filters offer high quality filtration for analytical samples. Certified for HPLC to ensure low extractables. Available in a broad range of membranes to meet sample compatibility requirements.
    How do I trap solvent vapors to prevent damage to my vacuum pump?
    The Sigma-Aldrich Glass Shop produces a number of different options to meet you lab's needs.
    Can you recommend a Solvent Extractor for organics from aqueous solution?
    For the quantitative extraction of organics from aqueous solutions and separations in immunoassays. The MIXXOR system has been applied successfully in many laboratory solvent extraction operations and is ideal for the rapid screening of alternative solvents for specific extraction problems.
    How do I effectively clean the inside and outside of my NMR tubes?
    The Sigma-Aldrich Dual-Action NMR Tube Cleaner (product Z414174-1ea ) simultaneously cleans tubes inside and out.
    What Vacuum Pumps are solvent resistant?
    The KNF Laboport vacuum pumps with solid PTFE heads and molded PTFE diaphragm and Kalrez® parts are resistant to chemical attack. (example product Z262250-1ea ).
    What is a useful Solvent for Recrystallization?
    "1-Chlorobutane - A Useful Solvent for Recrystallizations"
    David G. Morris, Ph.D., Department of Chemistry, University of Glasgow
    ACTA 34, NO. 2, 2001
    What is a good method for crystallization solvents?
    "Aldrich Rotary Evaporator Antisplash Adapters as Solvent Traps in Recrystallization"
    Mahesh K. Lakshman, Department of Chemistry, University of North Dakota
    ACTA 33, NO. 1, 2000
    How can solvents be removed from low melting crystals?
    "Moving Disc Filtration: Low-Temperature, Inert Atmosphere Removal of Solvent from Low-Melting Crystals in an Ordinary, One-Neck Flask"
    Roger C. Hahn, Associate Professor, Department of Chemistry, Syracuse University
    ACTA 31, NO. 3, 1998
    How can I prevent cross-contamination in my solvent still?
    "Preventing Cross-Contamination in Solvent Stills Connected in Series to the Same Inert Gas Manifold" Maravanji S. Balakrishna, Department of Chemistry, Indian Institute of Technology
    ACTA 33, NO.2, 2000
    Can Sigma-Aldrich dispense arrays of chemicals in custom formats for screening applications or parallel chemistry?
    When projects require a custom array of dispensed chemicals our packaging groups can custom pack reagents to your specifications. We call this service Discovery CPR. DiscoveryCPR offers the advantage of filling reagents in custom sizes. Using this option provides a cost benefit as well, you only pay for the amount you need. We have direct access to the Sigma-Aldrich catalogue containing over 80,000 items as well as another 130,000 items available through the Sigma-Aldrich Rare Chemical Library. Add our reagent outsourcing service and you have a virtually unlimited array of reagents at you disposal. We can package in millimole or milligram or gram aliquots. Information on our Discovery CPR service can be found here
    Or Email:
    What is special about the Rare chemical Library products that are shown in your catalogue?
    The Rare Chemical Library has 145,000 compounds consisting of: Private and academic collections released upon the researcher’s retirement
    Products no longer available from the Sigma Aldrich catalogues
    One time synthetic series from remote and obscure sources
    Synthetic analogues and precursors The price and availability of our rare chemical products is not available online. You can request this information from Technical Services. Email: Technical Service Information on the rare chemical library shown on our website can be found here

    • General
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    • RNAi
    • Oligos
    • Proteins, Enzymes & Proteomics
    Can I buy the individual parts included in kits as separate items?
    In many cases we do not supply the items included in kits as products that can be ordered individually, even though they have distinct part numbers, as it is commercially and logistically not feasible to do so. Please contact us if you have a specific enquiry. Email: Technical Service
    What grade of product should I choose for my application?
    Information on the different brands and grades of product that we offer can be found here There is also a tutorial available on searching for products:
    When a product is described as ‘cell culture tested’ what does this mean?
    Our cell culture testing is primarily a toxicity test for the product. For products that induce proliferation, the end results are slightly different. . During testing the material is sterilized (either sterile-filtered or autoclaved depending upon the product) regardless of whether the material is already sterile prior to testing. Unless the material is indicated as sterile-filtered, gamma irradiated, or indicated as sterility tested on the Certificate of Analysis, the product is not sterile as it is sold. Cell culture tested, insect cell culture tested, and plant cell culture tested products, all differ by the relevant cell species used, and the media used for the testing.  For ‘cell culture tested’ products, we use mammalian cells (such as CHO, L929, BHK, SP2, etc) in the recommended media, with the cells subjected to a specific product. The product is added, the media is filter-sterilized and then the cells are cultured for a total period of 2 weeks. At the end of this time, the cells are observed for effects on growth rate and morphology. It is expected that the material will not have any negative effects on the growth rate, or result in any changes in morphology. For ‘insect cell culture tested’ products, we use an insect cell line (Sf9) and insect media. The testing is the same as for cell culture tested products. For ‘plant cell culture tested’ products, we test plant tissue for growth in the recommended media that has been supplemented with the product. We grow for 2 weeks and look at the weight of the material and the physical appearance of the plant. The weight should be similar to the growth without the supplement and there should not be any obvious physical changes in the plant from the control.
    How do I adapt my cells to serum free culture?
    Some cell types may be sub-cultured directly into serum free medium. Others may require gradual induction over a number of passages. As adherent cells adapt to the serum-free medium, they will lift off the surface and become capable of suspension. Culture adaptation to serum free medium requires healthy, viable cultures in mid-logarithmic growth phase. 1. Using your normal seeding density and trypsinization procedures, subculture the cells into a mixture of medium containing 75% serum-containing medium and 25% of your specially formulated serum free medium Allow cells to reach normal confluency. 2. At the next subculture, passage the cells into a mixture of medium containing 50% serum-containing medium and 50% Serum free medium. Allow cells to reach normal confluency. 3. At the next subculture, passage the cells into a mixture of medium containing 25% serum-containing medium and 75% Serum free medium. At this point, most cultures will have lifted off the plate and will be capable of growth in shaker flasks. 4. At the next subculture, passage the cells into 100% serum free medium. Continue to subculture in serum free medium until the cells are fully adapted.
    My cells are not growing well and I suspect mycoplasma contamination what should I do?
    Sigma-Aldrich offers two products for the detection of mycoplasma contamination. Product MP0035 is based on a PCR methodology. Product MYC1 is based on staining of DNA. Either product can be used to confirm if mycoplasma contamination is present. We also have antibiotic selective reagents; (Ciprofloxacin 17850) and a kit (MP0030) that could be used in the elimination of mycoplsama contamination. Having said this, for anything but the most valuable cell lines, it would be most advisable to discard cultures as soon as mycoplasma contamination is suspected, and start the culture again. ECACC (The European Collection of Animal Cell Cultures, part of the HPA), offer a mycoplasma elimination service for valuable cell lines. For details contact ECACC Technical Support: 01980 612684.
    Do you sell media containing Glutamax?
    Glutamax is the brand name for a media supplement provided by another supplier. Our equivalent offering would be our AQ media which contains the dipeptide alanyl-glutamine, which is a more stable form of glutamine. We also offer alanyl-glutamine as a media supplement, product G8541.

    More information on the AQ media may be found here: AQ Media
    When should I use a gamma irradiated product?
    Frequently asked questions on gamma irradiation of products for cell culture
    How do I remove surfactants such as pluronic F68 from my serum free suspension cell medium?
    Information on removal of surfactants from serum free suspension media may be found here .
    Can Sigma-Aldrich offer samples of serum for batch testing?
    We have a dedicated telephone line for arranging serum batch tests tel. 0800 801640. Please contact us if you are arrangingserum batch tests and would like to be sent samples of some of our current batches to include in your trials.
    Are Sigma-Aldrich cell culture products CE marked?
    CE marking is now required in Europe, for cell culture media and equipment used in diagnostic testing. Our products, which are sold ‘for laboratory research purposes only’, are not CE marked. (Electrical items in the Labware catalogue are the exception to this and are CE marked in accordance with the appropriate regulations, for this type of product). The Sigma-Aldrich CE Marking Policy Statement can be found here.
    What is 9CFR AVA testing?
    Information on 9CFR AVA testing can be found here.
    Are Sigma-Aldrich Bovine serum products BSE tested?
    Information on BSE testing of Sigma-Aldrich products can be found here.
    Where can I find more information regarding the quality control testing that is performed on cell culture products?
    Information on the various quality control test methods used on Sigma-Aldrich cell culture products is available here.
    Do you offer custom media formulation?
    If you require a specific cell culture medium formulation that is not included in our range of catalogue items it is possible for us to prepare media to meet your requirements as custom items. There is however a minimum order volume of 200litres and a minimum order value of £2000 for custom media preparation.
    How long can I keep media once I have added serum and all the supplements?
    Once serum and supplements have been added cell culture media can be stored for at most ~6weeks in the fridge, and ideally less,. Media should be discarded if it becomes cloudy or changes in colour. The factors most likely to limit the lifespan of prepared cell culture media are the introduction of microbial contamination into the media, and the instability of glutamine. More information on glutamine stability can be found here.
    How can I get my chemical to dissolve in cell culture medium?
    Many of the compounds that we may wish to use in cell culture, only have limited solubility in aqueous solution, and so will not dissolve in cell culture media. As a general strategy for such chemicals we would advise initially preparing a concentrated stock in a solvent like ethanol or DMSO and then, once in solution, diluting the chemical to the working concentration in aqueous media. Ensure the final DMSO concentration does not exceed a toxic level to your cells. This strategy does not work in all cases and an alternative method of enhancing the aqueous solubility of hydrophobic compounds is to complex them with cyclodextrins. More information on cyclodextrins can be found here. Information on the solubility of various chemicals in water and in a solution of 2-hydroxypropyl beta-cyclodextrin, may be found here.
    How do I make up a powdered medium?
    Powdered media are extremely hygroscopic and must be protected from atmospheric moisture. If possible, the entire contents of each package should be used immediately after opening. Preparing the medium in a concentrated form is not recommended as some salt complexes may precipitate. Supplements that are added to the medium may affect shelf life and storage conditions. The basic steps for preparing the culture medium are listed below: Measure out approximately 90% of the final required volume of tissue culture grade water (Product No.W 3500), e.g. 900 ml for a final volume of 1000 ml. Select a container twice the size of the final volume. While stirring the water add the powdered medium and stir until completely dissolved. Heating may be required to bring powders into solution. Rinse the original container with a small volume of tissue culture grade water to remove traces of the powder. Add to the solution in Step 2. Add desired heat stable supplements (e.g. sucrose, gelling agent, vitamins, auxins, cytokinins, etc.) Add additional tissue culture grade water to bring the medium to the final volume. While stirring, adjust medium to desired pH using NaOH, HCl or KOH. If a gelling agent is used, heat until the solution is clear. Dispense the medium into the culture vessels before (or after) autoclaving according to your application. Add heat labile constituents after autoclaving. Sterilize the medium in a validated autoclave at 1 kg/cm2 (15 psi), 121 °C, for the time period described under Sterilization of Media Protocol. Allow medium to cool prior to use.
    Do I need to use heat inactivated serum?
    With modern production methods we would consider that use of a heat inactivated serum is not generally necessary, unless you are working with certain sensitive cell types, or immunological assays. Heat inactivation of serum which involves heating the serum to 56 degrees C for 30 minutes was historically performed as a method to kill off any viruses, bacteria and other adventitious agents in the serum. It also has the effect of destroying the complement fraction of the serum, and may result in lower overall levels of nutrients in the serum.
    How should I thaw and store Serum?
    Serum should be stored frozen at –20 degrees C, protected from the light, and should not be subjected to freeze thaw cycles. The method of thawing serum is also important in preventing the formation of precipitates. We would recommend taking bottles of serum from the freezer and allowing them to warm to room temperature for 10 minutes, then placing them in a water bath at 37 degrees C and swirling occasionally to prevent the formation of salt gradients as the serum thaws. More information on thawing and storing serum may be found here.
    Do you have any embryonic stem cell tested products?
    We have a wide range of products that we consider appropriate for use in stem cell culture. More information on products for use in stem cell culture may be found here.
    Are Sigma cell culture products manufactured to cGMP?
    The cell culture media products that Sigma-Aldrich offer are generally manufactured in a cGMP environment. The biochemicals and other reagents in the catalogue, however, are not manufactured to cGMP. If a cGMP product is required it is possible to order this as a custom item, but this is likely to be more expensive than purchasing a catalogue item.
    Which collagenase product should I use?
    Unfortunately, there is no general advice that we can give for the selection of an appropriate collagenase for the dissociation of specific cells. For some of our crude collagenases, we have cited references in the Sigma catalog under the product number, where it has been used with certain cells. Unless you can find a publication specifying a specific Sigma product number for your cells of interest, we can only advise that some experimentation may be needed to identify a product and batch that works best for your cells. A guide to collagenase products shown on our website may be found here.
    Can your HEPES modified media be used to culture cells on the bench?
    HEPES can be added to media to increase the buffering capacity and allow cells to be maintained outside a CO2 supplemented environment on the bench. The HEPES modified ‘classical’ media that we offer as catalogue items are, however, generally intended to be used in a CO2 supplemented environment. It should be noted that HEPES is likely to be toxic to cells at concentrations above 100mM.
    How do I resuscitate frozen cell lines?
    Cell culture stocks supplied by ECACC will normally be supplied to be stored frozen. In order to use them cells must be thawed and put into culture. It is vital to thaw cells correctly in order to maintain the viability of the culture. Some cryoprotectants such as DMSO are toxic above 4°C so quick thawing and dilution is essential to minimise toxicicity. Check the specific culturing requirements for your cell line. Prepare and label flasks with the cell line name, passage number and date. Wearing appropriate protective clothing, remove the ampule and place in a water bath at an appropriate temperature for your cell line (e.g. 37°C for mammalian cell lines). Submerge only the lower half of the ampule. Allow to thaw until a small amount of ice remains in the vial (usually 1-2 minutes). Transfer to a class II safety cabinet. Wipe the outside of the vial with a tissue moistened with 70% alcohol. Slowly dropwise pipette cells into pre-warmed growth medium to dilute out the DMSO. Incubate at the appropriate temperature for species and appropriate CO2 in atmosphere. Examine cells under a phase contrast microscope after 24 hours and subculture as necessary. For more ECACC handbook protocols click here .
    How do I subculture adherent cells?
    Adherent cell lines will grow in vitro until they have covered the surface area available, to produce a confluent momolayer, or until the medium is depleted of nutrients. At this point the cell lines should be sub-cultured in order to prevent cell death. To sub-culture cells they need to be brought into suspension. In most cases a protease such as trypsin is used to detach cells from the flask surface. In cases where cells may be damaged by proteases or it is important to retain membrane markers or receptors of interest, cell scrapers may be used to suspend cells. View cultures using an inverted microscope to assess confluency and confirm absence of bacterial or fungal contamination. Remove spent medium. Wash the cell monolayer with PBS without Ca2+/Mg2+ (product D8537), using a volume equivalent to half the volume of the culture medium. Repeat this step if cells are strongly adherent. Pipette Trypsin/EDTA (product T4049) onto the washed cell monolayer using 1ml per 25cm2 of surface area. Rotate the flask to cover the monolayer with Trypsin. Decant the excess Trypsin. Return the flask to the incubator and leave for 2-10 minutes. Examine the cells using an inverted microscope to ensure that all cells are detached and floating. The side of the flask may be gently tapped to release any remaining attached cells. Resuspend the cells in a small volume of fresh serum-containing medium to inactivate the trypsin. Remove 100-200µl and perform a cell count.(see question in this FAQ). Transfer the required number of cells to achieve the recommended seeding density for your cell line, to a new, labelled flask containing pre-warmed medium. Incubate as appropriate for the cell line. Repeat this process as demanded by the growth characteristics of the cell line. Key points.
    Trypsin is inactivated in the presence of serum and therefore it is important to remove all traces of serum from the culture medium by washing with PBS before addition of Trypsin. Prolonged exposure to Trypsin can cause damage to cells, cell clumping and cell death: Only incubate cells long enough for cell detachment. Trypsin should be neutralised with serum prior to seeding cells into new flasks or they will not attach. Trypsin inhibitor (product T6414) can be used to inhibit Trypsin in serum free culture. For more ECACC handbook protocols click here .
    How do I perform a cell count?
    For many cell culture applications including sub-culturing it is necessary to quantify the number of cells prior to use: Detach adherent cell cultures into suspension using Trypsin / EDTA (as per protocol above). Resuspend in a volume of fresh medium at least equivalent to the volume of Trypsin. Under sterile conditions remove 100µ to 200µl of cell suspension. Add an equal volume of Trypan Blue (product T8154). And mix by gentle pipetting. Clean the Haemocytometer. Moisten the coverslip with water (or exhaled breath). Slide the coverslip over the chamber back and forth using pressure until rainbow like rings appear (Newton’s refraction rings). Fill both sides of the chamber (5-10µl) with cell suspension and view under a light microscope using x20 magnification. Count the number of viable cells (appearing bright) and non-viable cells (stained blue). Ideally greater than 100 cells should be counted. Calculate the concentration of viable and non-viable cells. Where: A = The mean number of viable cells counted, i.e. Total viable cells counted divided by Number of squares. B = The mean number of non-viable cells counted, i.e. Total non-viable cells counted divided by the number of squares. C = The dilution factor. D = The correction factor provided by the haemocytometer manufacturer. Concentration of viable cells (cells/ml) = AxCxD Concentration of non-viable cells (cells/ml) = BxCxD Total number of viable cells = concentration of viable cells x volume Total number of cells = number of viable + number of dead cells. Percentage viability = (No of viable cells x 100) divided by Total number of cells. For more ECACC handbook protocols click here.
    What is the best way to look for antibodies and is it possible to search for secondary antibodies by species, isotype and conjugation?
    Antibody explorer provides a logical way of restricting searches of the website specifically to antibodies, and also allows you to search by target, species, isotype and conjugation, for primary, and secondary antibodies. There is also quick access to normal sera and purified immunoglobulins. Visit the Antibody Explorer tool on our website here.
    What albumin would you recommend for ELISA?
    Product A7030 Albumin from bovine serum would be recommended for use in ELISA. This product is of high purity and unlike many other albumin products it is essentially globulin free. This is important since contamination of blocking buffer with globulins may provide a source of background.
    Do you provide blocking peptides for your antibodies?
    We do not provide blocking peptides for our antibodies. We can however often provide details of the amino acid sequence that may have been used in generating an antibody. Please contact Technical Services if you require assistance with locating this information. Email: Technical Service. With this information it may be possible to have the relevant peptide made as a custom product by a company like New England Peptide or Eurogentec.
    Do you do trial size antibodies?
    We cannot supply antibodies in smaller amounts than the smallest pack size indicated in our catalogue for an item. We also do not supply free samples of antibodies. We have however been running a ‘No Risk Trial’ scheme to allow customers to try antibodies in applications that we may not have tested. More information on the ‘No Risk Trial’ can be found here.
    What is the concentration of my antibody?
    Most of our antibody products are tested for protein content as part of quality control and the protein concentration will be indicated on the Certificate of Analysis. The protein concentration may not be the exact concentration of the antibody since there may well be other contaminating proteins present. A more precise value for the immunoglobulin concentration is indicated on some products.
    Will my antibody cross react with other species?
    Any testing for cross reactivity of an antibody product with other species will generally be shown in the Product Information datasheet that may be available for the antibody product or in the description on the website. If cross reactivity with your cell species of interest is not indicated then it is likely that it has not been tested for that product.

    If the immunising sequence is indicated for the product, some indication of the likelihood of cross reactivity might be obtained by comparing the amino acid sequences, correlating to the immunising sequence in different organisms. If the amino acid sequence is conserved between species then it is likely that the antibody may well cross-react.

    Some antibody products are adsorbed with serum from other animals to reduce the potential for cross reactivity.
    How can I tell if an antibody will be suitable for my application?
    The applications in which an antibody has been tested will generally be included in the Product Information datasheet for the product or described on the Certificate of Analysis. If there is no information relating to your application of interest in these documents then it is likely that we have not tested the antibody in your specific application and will have no information available.
    If you want to test an antibody in a new application that we have not specifically tested it may be worth asking if we can offer a ‘No Risk Trial’ when placing your order. More information on the ‘No Risk Trial’ can be found here.
    What secondary antibody should I use?
    In choosing a secondary antibody to use it is important to consider in what animal the primary antibody was developed. If the primary antibody was raised in mouse then you will need and anti-mouse secondary antibody. You also need to consider the class, and sub-class of the primary antibody, the label, the form of the antibody that you require affinity purified or other, and various other factors. More detailed information can be found here.
    What antibody dilution should I use?
    The concentrations that we have used in the applications that we have tested will be found on the Certificate of Analysis for the product. The values may vary from batch to batch. To obtain optimal results, we would recommend titrating the concentrations of primary and secondary antibodies used in an application
    Do you have a protocol for use of the antibody?
    Protocols for a variety of antibody applications such as western blotting, ELISA, immunoprecipitation, immunohistochemistry and others can be found here. There are also a variety of laboratory manuals available such as ‘Using Antibodies: a Lab Manual’ by Harlow and lane (our product A8968-1ea) that contain protocols and useful information on using antibodies.
    What is the difference between a monoclonal and polyclonal antibody?
    In terms of their function, monoclonal antibodies recognise only a single epitope. Polyclonal antibodies are a mixture of immunoglobulins potentially recognising a number of epitopes.
    Do I need an affinity purified antibody?
    Most people prefer affinity-purified antibodies. These products are the most highly purified, and as a result give the lowest amount of non-specific binding. In certain cases IgG fractions may offer advantages. IgG fractions may contain very high affinity antibodies, that could be lost in affinity isolation, by binding so tightly to the affinity matrix that they are not eluted. IgG fractions may be useful in situations where very high affinity is required; most commonly when the antigen of interest is rare or present in low abundance.
    When should I use a F(ab’)2 fragment?
    If working with tissues or cells that have Fc receptors (thymus, spleen, blood, leukocytes, B cells etc.), choose an F(ab )2 fragment when possible to eliminate non-specific binding through Fc receptors present on cells. Alternatively, Fc receptors can be blocked. To do this, perform an absorption step using purified IgG from the host species of the your secondary antibody. In that case an F(ab)2 secondary antibody may not be necessary.
    What label should I choose?
    The choice of label is extremely application dependent. For immunoblotting and ELISA, enzyme-labeled secondary antibodies are most popular. In general, peroxidase is economical, rapid and a more stable enzyme than alkaline phosphatase. It has also become very popular for use in chemiluminescent detection systems. Alternatively, alkaline phosphatase is considered more sensitive than peroxidase, particularly when colorimetric detection is used.

    For cell or tissue staining, alkaline phosphatase, peroxidase or fluorescent secondary antibodies may be used for cytochemistry or histochemistry. Secondary antibodies labelled with a fluorochrome (FITC, phycoerythrin, and Quantum Red) may be used for flow cytometry.

    To generate an increase in amplification and consequential fluorescence signal, a two-step biotin/avidin system could be used. Biotin binds with very high affinity to avidin resulting in an essentially irreversible interaction. A biotinylated secondary antibody is applied first, followed by avidin, ExtrAvidin, or streptavidin conjugated to an enzyme or fluorochrome. This binds to multiple sites on the biotinylated secondary antibody, thus amplifying the signal and resulting in greater sensitivity than that achieved with an antibody-enzyme or antibody-fluorochrome conjugate alone.
    What substrate should I choose?
    The choice of substrate to use with an antibody depends on the enzyme that is conjugated to the antibody (most often alkaline phosphatase or peroxidase), and the application in which the antibody is to be used (western blotting, ELISA or immunohistochemistry). Information and comparison of the different substrates that are available for applications can be found following the links below:
    Why would I choose a whole molecule FAB specific, or Fc specific, or light chain specific antibody?
    Polyvalent antibodies react with all classes.
    Fc and heavy-chain specific antibodies only react with heavy chains and are, therefore, class specific (i.e. gamma chain specific reacts only with IgG; µ chain specific reacts only with IgM, etc.) Fab and whole molecule (wm) specific antibodies react with heavy and light chains. Due to the light chain reactivity, they can react with all classes. Light chain (kappa, lambda) specific antibodies react with all classes, since all classes use the same kappa or lambda light chains.
    What is the difference between protein A, protein G and protein L?
    A table comparing the efficiency of binding to protein A, G and L, for immunoglobulins from different organisms and of different isotype can be found within the datasheet for product P1301. A link to this datasheet is included here:
    When a product is described as “for molecular biology”, what does this mean?
    Products described as molecular biology grade are tested for the presence of nuclease (DNase and RNase) activity as standard.
    I am having trouble with my SDS PAGE can you help?
    An SDS PAGE gel trouble-shooting guide is available here.
    How can I reduce RNase contamination?
    A quick reference guide to reducing RNase contamination is available here.
    What is the difference between the various E.coli strains available?
    Laboratory E.coli strains stains have a numerous genetic modifications to improve their functionality in order to best identify the strain most suited to your application. There is a list available of the significant genetic markers here.
    Where can I find information on ordering and pricing for shRNA products?
    All of Sigma's shRNA clones can be conveniently ordered on our website. More information on placing orders or for pricing information, can be found here.
    Can I order shRNA products in a custom format?
    We are pleased to offer custom services for customers requiring large volumes or special orders. More information on custom shRNA products can be found here.
    Where can I find more information on TRCDesign and the pLKO.1 Vector?
    The MISSION shRNA clones, designed by the TRC, are pre-cloned into the pLKO.1-Puro vector. This lentiviral vector allows for propagation in bacterial culture and selection of inserts in mammalian cells. More information about shRNA or vector design can be found here .
    What formats are available for shRNA clones?
    Whole-genome TRC shRNA libraries, gene family sets or individual shRNA clones are available in the following three options: lentiviral particles, plasmid DNA and bacterial glycerol stocks. For more information about each of these formats, please follow the links below.
    Where can I find more information about Experimental Design & Analysis
    For common questions regarding experimental design and analysis or for a list of validated cell types, please select one of the links below: Experimental Design Validated Cell Table Analysis
    Where can I find more information on Advanced RNAi Applications?
    For more information regarding in vivo applications or use of these products within difficult cell types, please select one of the links below:
  • in vivo
  • Difficult Cell Types
  • Where can I find more information about the ExpressMag, Transduction Enhancement System?
    The ExpressMag system consists of magnetic beads that are designed to improve the lentiviral delivery of genetic information into target cells that are difficult to transduce. The ExpressMag System has been specifically validated to support the MISSION lentiviral shRNA products. More information on the ExpressMag system can be found here.
    How can I contact an expert on RNAi , I have a question that is not covered in the frequently asked questions?
    If you have a question that you would like to have answered by an RNAi Expert please Email:
    Who do I contact with questions about library pricing, to obtain a quotation, or with other concerns?
    For technical questions, pricing, a quotation or to arrange a visit or even a presentation from one of our specialists please contact or Technical Service.
    How does Sigma quantitate oligos?
    We carefully measure the O.D. value of custom oligos using a UV spectrophotometer. Additional information regarding the equations used to determine the O.D. value are available, following the link below:

    Quantitating DNA
    I ordered a 0.2 µmole scale oligo. Does this mean that I will receive 0.2 µmole of product?
    The scale of synthesis represents the µmole of starting material for the first base of synthesis. The overall µmole yield of full-length oligonucleotide depends on the average coupling efficiency of each base and on the number of couplings (length of oligo). Sigma quotes a coupling efficiency of 98-99%. Yields of full-length oligonucleotides can vary considerably based on length and type of purification requested. Sigma has set standard minimum yield guarantees based on the synthesis and purification of your oligo. The minimum guaranteed yields are based on absorbance at 260 nm (optical density units or O.D.s) rather than µmole amounts. Information on the yields of oligos for different scales of synthesis can be found here.
    What oligonucleotide modifications does Sigma offer?
    Sigma offers numerous oligonucleotide modifications including biotin, terminal amines, terminal phosphates, fluorescein, 6-FAM, HEX and TET just to name a few. For specific modification requests please Email:
    I received my oligonucleotide but there seems to be nothing in the vial. Where is the oligonucleotide?
    All oligos are provided dry unless otherwise specified. It may be difficult to see the oligo in the bottom of the vial, since it may be present as a clear film coating the vial surface. You can be assured that the oligo is in the vial with the quantitative information located on the vial label. We recommend quickly spinning each vial prior to opening. Measuring the absorbance of the oligo at 260nm in a spectrophotometer can confirm concentration after reconstitution.
    What purification methods are available?
    Desalting: Every oligo is desalted free of charge to remove residual by-products from synthesis RP1 (reverse-phase cartridge): Cartridge purification provides 80-90% pure full-length product. HPLC: Provides 90-97% full-length product and is the method of choice for purifying larger quantities of oligos (>1 mmol scale of synthesis). Poly-Acrylamide Gel Electrophoresis (PAGE): Provides 95-99% of the full length product. Additional information on the different types of oligonucleotide purification available can be found here.
    When designing my oligo, should I locate modifications at any specific site?
    We recommend 5' modifications when possible; however 3' and internal modifications are also available.
    What are the recommended storage conditions for oligonucleotides?
    We recommend storage of oligonucleotides at 2-8°C in the fridge short-term (1-2 weeks). For intermittent use, store at –20°C. An important consideration in oligo stability is to prepare stock solutions with nuclease-free sterile water or 1x TE buffer. Fluorescently labeled oligos should be stored in the dark protected from the light. Additional information on handling and storage of oligonucleotides can be found here.
    How does Sigma calculate the melting temperature (Tm) of oligonucleotides?
    The melting temperature (Tm) is calculated using the nearest-neighbour method. The factors that affect the Tm of an oligo in an application include: salt concentration, strand concentration, the presence of denaturants as well as the sequence and the length of the particular oligonucleotide. Sigma uses standard PCR conditions to determine the Tm (50 mM NaCl and 0.5 µM oligonucleotide). Additional information on melting temperature can be found here .
    Can Sigma provide two DNA oligonucleotides annealed together?
    We do not offer DNA annealing as a service. A protocol for annealing oligos can however be found here.
    Does my oligonucleotide have a phosphate on the 5' or the 3' end?
    All of our custom oligonucleotides are synthesized with a hydroxyl group on both the 3’ and 5’ ends. However, if requested, we can synthesize your oligo with a 5’ and/or 3’ phosphate.
    What is the longest oligonucleotide that Sigma will synthesize?
    Sigma can synthesize oligos as long as a 130-mer. Please note that yield and quality can be affected by base composition. Oligos greater than 110 bases can only be synthesized on the 1.0 µmole scale.
    If I left my oligos on the lab bench over the weekend, will they still work?
    Dry oligonucleotides have tremendous stability. Oligos in solution have a more finite shelf-life. For most situations, resuspended oligos should still work well, even if left at room temperature for a couple of days.

    Additional information on handling and storage of oligonucleotides can be found here: You and Your Oligo
    Does Sigma offer oligonucleotide design assistance?
    Our technical staff routinely assist researchers with primer design. Additionally, you may determine the melting temperature, molecular weight, GC content, significant structure and primer dimmer by using the online calculations feature: DNA Calculator: If you have additional questions, please contact our technical support group. Email:  For help with designing dual labeled probes see here.
    How do I make a 100 µMolar stock solution of my oligo?
    Sigma provides quantitative data on your oligo using nmoles, optical density units (O.D.) and micrograms. This allows simple preparation of stock solutions for whatever units you prefer. A general rule states that for any oligo, the number of nmoles x 10 will give you the amount of solvent to add in microliters for a 100 µM stock solution. 100 µM is also equal to 100 pmol/microliter for those who wish to work with pmole amounts. Additional information on handling and storage of oligonucleotides can be found here
    I ran oligo on an agarose gel but cannot see anything, why?
    Visualization of single stranded oligonucleotides in electrophoresis using ethidium bromide as a stain depends on the secondary structure of the oligonucleotide, since the dye binds to double stranded DNA. The sequence is also important with AT rich oligos not staining well. We would recommend analysing oligos on an acrylamide gel (perhaps 13-18% depending on the length of the oligo) and staining with ‘stains-all’, silver staining or perhaps using SYBR green. For quantitation of oligos we would recommend measuring the OD at 260nm in a spectrophotometer.
    There is a white precipitate in my HPLC purified oligos, why?
    This is sometimes common after freeze-drying of larger quantity of the oligo. The precipitate is the inert material, which does not affect the quality of the oligonucleotide, and if required can be spun down and discarded.
    My PCR is not working, why?
    There are number of things that can affect the performance of PCR reactions. To exclude the oligonucleotides as the source of the problem you might want to check: 1) The sequence of the primers that you are working with, and whether primers with these sequences have been shown to work previously with same conditions. 2) If  the vial containing the oligo was spun to make sure that the pellet was at the bottom before solubilisation? 3) Was the concentration of the oligonucleotide as measured at 260nm in a spectrophotometer, in accordance with the determined on quality control sheet supplied with the oligos?
    I found error(s) in long desalt oligos after cloning, why?
    All oligos prepared by Sigma Life Science are analysed by mass spectrometry as part of quality control. The smallest mass difference in any single base-substitution is 9 Da (A for T). Our MS instruments routinely achieve 0.05% precision, which provides a mass difference of 3.25 Da for a 20mer primer. This is well under the 9 Da difference associated with a worst-case base switch. Related to answer an above, the smallest mass weight of any single base (insertion or deletion) is 304 Da (T). Mass differences of this magnitude are well above the 0.05% mass accuracy and are readily detected. Since 100% of oligos are analysed by mass spectrometry this should provide our customers with 100% assurance that insertions/deletions/substitutions will be caught within our QC systems and rejected. As DNA synthesis is a step-wise manufacturing products with a 99.4% coupling efficiency, there are fractional amounts of species where the normal capping step is incomplete. For most applications, these ppm-level products pose no effect. However applications such as cloning and sequencing should always use a highly purified product to prevent even 1 copy of these minority species from being incorporated into the vector or plasmid. For this reason, Sigma strongly discourages the use of desalt grade oligos for cloning and recommends PAGE. In the small number of cases where customers have used our products and observed some mutation or deletion in their clones, we always re-manufacture these at no additional cost.
    Does an oligo need a 5' phosphate group for ligation (and) does the oligo come with one?
    Does an oligo need a 5' phosphate group for ligation (and) does the oligo come with one? 5’ phosphate groups are required for ligation of oligos. Sigma life science oligos are supplied with OH groups at the 5’ and 3’ ends as standard. Phosphate groups can be requested at either the 5’ or 3’ end as an additional modification.
    Is it ok to leave oligos at 4 deg C in solution for several weeks...?
    We would not recommend storing oligos in solution in the fridge for longer than a week, to avoid degradation. We recommend oligos to be stored in aliquots at –20oC or –80oC degrees.
    For a qPCR probe, what can I use instead of NED or VIC?
    We would suggest that Cy3 might be used as an alternative to NED, and VIC could be replaced by Hex.
    How do I convert from International Units to Sigma units?
    It may not always be possible to convert between different unit definitions for a product. USP units are generally equivalent to International units, but for other conversions it may be advisable to contact Technical services for more details. Email: Technical Service
    My product is sold in units, what weight will I receive?
    Although sold in terms of units a value for the number of units per mg of solid, or per mg of protein and purity will often be indicated on the certificate of analysis for each batch. The weight of material can be calculated from this. If in doubt please contact Technical Services for assistance: email Technical Service or within Germany Tel 0180 223 7135.
    What do the different Typings indicated for Sigma enzymes mean?
    Many enzyme products offered by Sigma will include a ‘Type’ in the description (e.g. collagenase type I). These typings are generally ‘internal’ Sigma typings indicating a different source or method of manufacture for a product and may have no biological significance. Care should be taken not to confuse ‘Sigma typings’ with recognised classifications from the literature (e.g. Bornstein and Traub typings for collagen).
    Where can I find frequently asked questions on HIS Select products?
    Frequently asked questions for HIS SELECT products can be found here: HIS Select FAQ

    • General
    • Glassware
    • Consumables / Plasticware
    • Electronic Equipment
    • Software / Books / Educational
    • Safety Equipment
    • Manufacturers
    There is not much information about my product on the website. Where can I find more information?
    Sigma-Aldrich are distributors rather than manufacturers, for most of the Labware items and thus have limited information available. Where the manufacturer of the Labware item is obvious, we would recommend that more information can often be found by visiting the supplier website. Alternatively you can contact technical services on Tel 0800 8000 80 or email us at Technical Service and we can help find more information for you.
    What do needle gauge sizes indicate?
    A needle gauge conversion chart with dimensions for various gauges indicated can be found here: Syringes Needle Guage Chart
    Where can I find information on converting between various units?
    Information relating to the conversion between various units of volume / pressure absorbance and percentages / ppm can be found here
    Where can I find the Aldrich Technical Bulletins?
    The Aldrich Technical Bulletins can be found here: Technical Bulletins
    Can you send me a user manual for a product?
    To obtain the appropriate manual if there is one available from the supplier, please contact Technical Services. Email: Technical Service.
    Can Sigma-Aldrich offer servicing, repair or spare parts for equipment?
    Unless specifically indicated in the catalogue Sigma-Aldrich do not offer spare parts or servicing of their Labware products. We recommend contacting the relevant manufacturer directly for servicing or spare parts.
    Are Sigma-Aldrich cell culture products CE marked?
    CE marking is now required in Europe for cell culture media and equipment used in diagnostic testing. Our products, which are sold for laboratory research purposes only, are not CE marked. (Electrical items in the Labware catalogue are the exception to this and are CE marked in accordance with the appropriate regulations, for this type of product). The official CE marking policy statement for Haematology and Histology products is available here: CE Marking Policy
    Why can't I order PYREX® brand products from Sigma-Aldrich in the UK
    As a result of licensing issues Sigma-Aldrich are not able to distribute in Europe many of the PYREX® brand products listed on our website, although these products are available to customers in the USA.

    Exceptions to this are some of the PYREX® items sourced from Corning. These products may be identified by the format of the product number that will start with CLS (e.g CLS44501L PYREX® disposable centrifuge tube, ungraduated).
    How do I ensure that I get a UK format 3 pin plug on equipment from Sigma-Aldrich?
    For electrical Labware items the voltage, plug format and regulations around these, vary from country to country. In order to ensure that these items are sent out in the correct format for the UK, the product code of many items is suffixed with 'GB e.g. Z637637GB-1EA, Accujet pro-pipette controller. Please ensure that you state the ‘GB’ when placing the order.
    Where only a European 2 pin plug model for a piece of equipment is available can I buy an adapter
    Occasionally we are only able to offer a product in a European plug format. Where this is the case we are not able to offer plug adapters.
    Why can't I order PYREX brand products from Sigma-Aldrich in the UK?
    As a result of licensing issues Sigma-Aldrich are not able to distribute in Europe many of the PYREX® brand products listed on our website, although these products are available to customers in the USA.

    Exceptions to this are some of the PYREX® items sourced from Corning. These products may be identified by the format of the product number which will start with CLS. (example CLS44501L PYREX® disposable centrifuge tube, ungraduated).
    Can I get glassware custom made or repaired?
    Information on the custom glassware manufacture service offered by Sigma-Aldrich can be found here. Please contact us on 0800 272572 or Email: Technical Service and we can direct your enquiry in the right direction.
    What do the numbers in the joint sizes actually indicate?
    The number format of glass joints are normally presented as follows: (e.g. 24/40). The first number represents the outer diameter (OD) in millimeters (mm) at the base (widest part) of the inner joint. The second number represents the ground glass length of the joint in millimeters. The most common joints are 14/20 and 24/40. There are also European ISO standard joints with common joint sizes of 10/19, 14/23, 19/26, 24/29 and 29/32. The US and ISO joints differ only in the length not in the slope, and can be used in combination with one another.
    How can I find out if vials are sterile or DNAse, RNAse, pyrogen free?
    In most cases the product description on our website will state whether they are DNAse, RNAse and Pyrogen free. If you are unsure, then you can contact us on 0800 272572 or Email: Technical Service.
    What is the difference between a Luer Lock and a Luer Slip tip syringe?
    Luer-Lok fittings are securely joined by means of a tabbed hub on the female fitting which screws into threads in a sleeve on the male fitting. Luer-Slip fittings simply conform to Luer taper dimensions and are pressed together and held by friction (they have no threads).
    My regulator doesn’t seem to fit Aldrich gas bottles.
    Sigma-Aldrich always recommends using our own regulators with the gas bottles we supply. Most of our gas bottles and cylinders have US based dimensions and may not always be compatible with other brands of regulators or control valves. Useful information on gas regulator selection and installation can be found here.
    Should I use a gas regulator or a control valve?
    This will depend on whether you are trying to maintain pressure within a closed system or wanting to dispense gas directly and control the flow. For maintaining pressure within a closed system it is recommend to use a regulator so you can regulate the gas flow. If you just want to dispense, then a control valve should be suitable.
    Are Sigma-Aldrich cell culture products CE marked?
    CE marking is now required in Europe, for cell culture media and equipment used in diagnostic testing. Our products, which are sold for laboratory research purposes only, are not CE marked. (Electrical items in the Labware catalogue are the exception to this and are CE marked in accordance with the appropriate regulations, for this type of product).

    The official CE marking policy statement for Haematology and histology products: CE Marking Policy
    How do I ensure that I get a UK format 3 pin plug on equipment from Sigma?
    For electrical Labware items the voltage, plug format and regulations around these, vary from country to country. In order to ensure that these items are sent out in the correct format for the UK, the product code of many items is suffixed with 'GB e.g. Z637637GB-1EA, Accujet pro pipette controller. Please ensure that you state the ‘GB’ when placing the order.
    Where only a round European 2 pin plug model for a piece of equipment is available can I buy an adapter?
    Occasionally we are only able to offer a product in a European plug format. Where this is the case we are not able to offer plug adapters.
    What type of pH electrode should I use?
    A guide to the selection of an appropriate pH electrode can be found here: Electrode Selection
    Where can I obtain a metabolic pathway, or periodic table poster?
    The “Metabolic pathways” poster is sold as a catalogue item with product number M3907. We also offer the “Inborn errors of metabolism” poster which has product number I8014.

    The Periodic table of the elements poster is product Z543209.

    These products are also available as smaller charts.

    More information on the metabolic pathways chart and relevant animations can be found here Metabolic Pathways
    Do you have any products that could be used to demonstrate various principles of chemistry to schoolchildren?
    We do have a range of chemistry demonstration kits available to demonstrate, for example:
    • Chemically activating a bulb
    • Chemiluminescence
    • Combustion of magnesium in Air and Carbon dioxide
    • Conductivity in solutions
    • Crystallization from Supersaturated solutions
    • Electrolysis of water
    • Gas solubility-Ammonia Fountain Effect
    • And Oxidation of metallic iron in Agar-Agar gel.
    A list of educational aids that we offer can be found here.
    Where can I find information on your Spectral Viewer product?
    Frequently asked questions relating to Spectral Viewer can be found here.
    What is the ISBN number?
    The International Standard Book Number (ISBN) is a unique numeric commercial book identifier based upon the 13 digit Standard Book Numbering (SBN) code.
    What type of respirator do I need to use with my chemicals?
    We have a range of disposable and reusable respirators available. It important when choosing a respirator for use in your working environment to consider the type of respiratory hazard that you are protecting against; Is it dust and is it toxic or non toxic, or is it organic vapours or acid gas? You also need to consider the concentration of the chemical or particles in the air, and how these relate to personal exposure limits. Information on respirators can be found here.
    Which spill kits do you offer?
    We offer a range of spill kits for dealing with chemical spills around the laboratory. Please click here to find out more. Of the products listed here only Z228443 is indicated as suitable for dealing with solutions of hydrofluoric acid. Information on other products for spill control can be found here.
    I have the Corning product number for an item. How do I find the Sigma-Aldrich catalogue number?
    If you have the Corning part number, add CLS in front of this when searching on our website and it will take you to the correct product.
    Where can I find the supplier details?
    In some cases we mention the supplier on our website and sometimes provide a manufacturers part number. If we do not mention the supplier on our website you can always contact us on Tel 0800 27 25 72 or Email: Technical Service.

    In some cases our supplier information is considered proprietary.