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How does Sigma quantitate oligos?
We carefully measure the O.D. value of custom oligos using an UV spectrometer. Additional information regarding the equations used to determine the O.D. value is available: Quantitating DNA.
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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 oligo 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. Yield Chart
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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 contact dnaoligos@sial.com.
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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. You can be assured that the oligo is in the vial with the quantitative information located on the vial label. We recommend that you quick spin each vial prior to opening.
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What purification methods are available?
Several types of purification are available (see also Oligonucleotide Purification):
- Desalting: Every oligo is desalted free of charge to remove residual by-products from synthesis deprotection and cleavage.
- 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% full length product.
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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.
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What are the recommended storage conditions for oligonucleotides?
We recommend you store oligonucleotides at 4°C for short term use (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 light-free conditions. For additional information, see You and Your Oligo.
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How does Sigma calculate the melting temperature (Tm) of oligonucleotides?
The melting temperature (Tm) is calculated using the nearest-neighbor 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). For additional information: Melting Temperature.
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Will Sigma anneal two DNA oligonucleotides?
We do not offer DNA annealing services. Protocol for Annealing Oligos
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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.
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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.
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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. More information: You and Your Oligo.
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Does Sigma offer oligonucleotide design assistance?
Our technical staff routinely assists 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 (oligotechserv@sial.com)
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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. For additional information on resuspending and handling oligos: You and Your Oligo.
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