Working with BRAND® Liquid Handling Instruments

The ever increasing demands on the quality of analytical results, and the growing number of samples to be processed result in a need for volumetric instruments which help to handle the routine work in sample preparation as efficiently as possible. Manufacturers of laboratory equipment have responded to this need by developing specialized liquid handling instruments. These appliances represent an improvement over the traditional volumetric instruments made of glass or plastic, and allow efficient work with a superior degree of precision and ease of operation.

The liquid handling instruments from most manufacturers share a similar operating principle, however the design details and materials used differ somewhat from one manufacturer to the next. On the following pages, we will explain the functional principles and application of some of the most common liquid handling instruments, using appliances made by BRAND® as examples.

Working with Liquid Handling Instruments

Working with Liquid Handling Instruments

Dispensing with bottletop dispensers

Definition of 'dispensing':

The term 'dispensing' is understood to mean the discharge of defined quantities.

For easy, rapid and precise dispensing of reagents, bottletop dispensers are widely employed to replace poured transfers into gratuated cylinders. They can be mounted directly on commercial laboratory bottles, either directly or by means of adapters. It is no longer necessary to transfer or decant chemicals. Serial dispensing in particular is greatly facilitated.

Functional principle of bottletop dispensers

By an upward movement of the piston, the preset amount of liquid is aspirated from the reagent bottle into the dispenser cylinder. By the subsequent downward movement of the piston, the liquid is released through a valve system and the discharge tube. There is no need to set a meniscus or to observe a waiting time.

We distinguish between bottletop dispensers with floating piston and with wiping-seal piston.

Functional principle of bottletop dispensersFunctional principle of bottletop dispensers

Bottletop dispensers with floating pistons

This system requires no piston seal and is therefore very durable and maintenance-friendly. The piston fits into the dispensing cylinder without contact. Piston and cylinder are separated by a gap only a few thousandths of a millimeter wide and filled with liquid. This film of liquid acts as a lubricant which makes the piston glide very smoothly.

e.g., Dispensette® by BRAND®

Bottletop dispensers with floating pistonsRange of application

For dispensing aggressive reagents, e.g., concentrated acids such as H3PO4, H2SO4, bases like NaOH, KOH, saline solutions, as well as many organic solvents: Dispensette® S

For dispensing organic solvents, such as chlorinated and fluorinated hydrocarbons (e.g., trichlorotrifluoroethane and dichloromethane), or acids such as concentrated HCl and HNO3, as well as for trifluoroacetic acid (TFA), tetrahydrofuran (THF) and peroxides: Dispensette® S Organic

For dispensing HF we recommend the use of the Dispensette® S Trace Analysis with platinum-iridium valve spring.

Materials

Depending on the requirements, parts that come into contact with liquid are made from various specially resistant materials, e.g., ceramic, platinum-iridium, tantalum, ETFE, PFA.

Safety always comes first!

When choosing a bottletop dispenser, the safety features of the instrument should be kept in mind. For example, does it reduce the risk of injury due to glass breakage? How does it avoid accidental splashing when the instrument is primed? How is contact with the medium minimized when the dispensing tube is closed?

Likewise, the suitability of the dispenser for the medium to be dispensed should be checked by the user. Information about this can generally be found in the operating manual in the chapter 'Function and limitations of use'. When in doubt, contact the manufacturer directly. Information on maintenance and monitoring of measuring instruments are also found in the operating manual.

 

 

 

Monitoring of measuring instruments / calibration

In regard to the monitoring of measuring instruments according to ISO and GLP guidelines, the accuracy of volumetric instruments should be checked regularly and recalibrated if necessary (see page 33).

Bottletop dispensers with wiping-seal piston

Bottletop dispensers with wiping-seal pistonIn addition to the 'floating piston' operating principle, instruments with 'wiping-seal' piston are also used. It is frequently reported that these systems require higher operating forces and that the frictional wear can cause defective seals.

e.g., seripettor® by BRAND®

The design of the system allows a replacement of the complete dispensing cartridge. The somewhat higher operating forces during filling are minimized by a spring with automatic lifting action. The present example reflects a competitively-priced dispenser for simple dispensing tasks in the volume range of 0.2 to 25 mL.

Range of application and materials

The range of application includes the daily routine dispensing of bases, acids in low concentration, biological buffers, cell culture media, biological detergents and polar solvents.

Titrating with bottletop burettes

Definition of 'titration':

Titration is a volumetric method used for the quantitative analysis of a dissolved substance.

How to titrate?

Using a bulb pipette, a defined portion of a sample (liquid with an unknown fraction of dissolved material, e.g., acetic acid) is placed in an Erlenmeyer flask. After dilution with water, 3 drops of an indicator solution are added. Then, with continuous swirling, a suitable titrant of known concentration (e.g., 0.1 M NaOH) is added from a burette until a color change in the indicator signals the endpoint of the titration. Using the chemical equation and the volume of titrants used, the amount of substance dissolved in the sample can be calculated.

Titrating with bottletop burettes

Titrating with bottletop burettesFunctional principle of bottletop burettes

Bottletop burettes are mounted directly upon the reservoir bottle. By the upward movement of the piston, liquid is aspirated from the reagent bottle into the burette cylinder. By the subsequent downward movement of the piston, the liquid is released slowly, and added to the sample through the discharge tube until the titration is finished, e.g., by change of color.

Reading the volume

The discharged volume can be read directly from the display of the bottletop burette. There are no meniscus reading errors.

e.g., Titrette® by BRAND® in 10 mL, 25 mL, and 50 mL sizes

The piston moves when the hand wheels are turned, and this takes up or discharges the liquid. The electronics of the instrument automatically recognize the direction of rotation, whether filling or titration is taking place. The liquid can be taken in quickly, and can then be delivered exactly, very slowly, drop by drop. A recirculation valve makes it possible to run the liquid back into the bottle during priming. Thus, air bubbles can be removed without loss of medium. The instrument can readily be disassembled in the laboratory for cleaning and maintenance.

Range of application

It can be used in many applications for aqueous and non-aqueous solutions (e.g., alcoholic KOH) up to 1 M.

Reading the volume

Materials

Parts that come into contact with liquid are made from various specially resistant materials, e.g., borosilicate glass, PTFE, platinum-iridium, Al2O3 ceramic.

Pipetting with air interface pipettes

Definition of 'pipetting':

Pipetting is the accurate one-time uptake and delivery of liquids.

An air interface pipette is used for pipetting aqueous liquids in the microliter to milliliter range. It operates by the air interface principle.

Functional principle

The up and down movement of the piston inside the pipette shaft creates a negative or positive pressure of the air column. As a result, liquid is either aspirated into the tip or expelled from it. The air column (air interface) keeps the liquid separated from the piston.

Pipetting with air interface pipettes

Benefits

There is no wetting of the instrument; the liquid only enters the tip. Tips are used only once, which eliminates any carry-over. This is particularly important for applications where sterile conditions are required, or no carry-over is allowed.

Calibration

In regard to the monitoring of measuring instruments according to ISO and GLP guidelines, the accuracy of volumetric instruments should be calibrated regularly (i.e. checked) and adjusted if necessary (see page 33).

Manual single-channel pipettes

e.g., Transferpette® S by BRAND®

In the routine lab and in research, precision and functionality are the standards to expect from air interface piston-operated pipettes today.

"Manual

Operation

Air interface piston-operated pipettesAir interface piston-operated pipettes

Manual multichannel pipettes

These pipettes also function by the air interface principle. They allow 8 or 12 pipetting operations to be carried out simultaneously.

Microtiter technology requires pipetting into microtiter plates of 8 x 12 cavities (96-well plates) with standardized spacing. This technology allows e.g., the detection of minute quantities of proteins. This method can only be employed efficiently with multichannel pipettes. Multichannel pipettes are ideal for the efficient transfer of samples, for serial dilutions and for washing of microtiter plates.

Areas of application Analytical techniques
  • Clinical diagnostics
  • Immunofluorescence (IF)
  • Food analysis
  • Radio immunoassay (RIA)
  • Immunology
  • Enzyme immunoassay (EIA, ELISA)
  • Biochemistry
  • Cell culture dilution
  • Cell culture
  •  

    Manual multichannel pipettesManual multichannel pipettes

    e.g., Transferpette® S -8/-12 by BRAND®

    Operation

    Manual multichannel pipettes

    Ergonomics and Strain

    Intensive, repeated operations done on mechanical instruments without proper ergonomic design result in prolonged stress that can lead to a number of muscular problems, known collectively as RSI (repetitive strain injuries). At particular risk are the muscles in the neck area,  shoulders, arms and thumbs. Thus, laboratory work is often accompanied by the appearance of, inter alia, tendonitis and carpal tunnel syndrome. Especially with microliter pipettes, the need for fatigue-free operation is paramount.

    Electronic single- and multichannel pipettes

    Operating principle

    Pressing the pipetting button starts the aspiration or discharge mechanisms (incl. blow-out). The pipette’s piston is moved by a motor, aspiration and discharge are controlled by a microprocessor. Various pipetting programs can be selected with the control keys.

    Advantages of electronic pipettes

    The combination of motor-controlled pipettes and ergonomic design enables stress-free, fatigue-free operation. It also reduces the demands on the thumb while carrying out lengthy series which would otherwise increase the risk of RSI syndrome! An additional advantage is the execution of pipetting programs such as the gel electrophoresis mode (with precise display of delivered volume) and a dispensing mode, which are not possible with manual pipettes.

    Advantages of electronic pipettes

    The combination of motor-controlled pipettes and ergonomic design enables stress-free, fatigue-free operation. It also reduces the demands on the thumb while carrying out lengthy series which would otherwise increase the risk of RSI syndrome!

    An additional advantage is the execution of pipetting programs such as the gel electrophoresis mode (with precise display of delivered volume) and a dispensing mode, which are not possible with manual pipettes.

    Advantages of electronic pipettes

    With electronic single- and multichannel pipettes, handy design, balanced weight distribution, intuitive software and clear, readily understood technical documentation should be standard.

    Discharge reagent

    Place the pipette tip against the wall of the vessel. Hold the pipette at an angle of 30-45° relative to the container wall and press the pipetting button again – the liquid will be discharged. The blow-out takes place automatically! During this process, wipe the tip on the vessel wall.

    Eject tips

    Press the tip ejector.

    Pipetting programs of the microliter pipette Transferpette® electronic

    Pipetting programs of the microliter pipette Transferpette® electronicPipetting programs of the microliter pipette Transferpette® electronic

    Program for mixing of liquids Pipetting
    The standard program. The set volume is aspirated by the pipette, and then discharged.
    Depending on the quality and design, electronic pipettes can offer further instrument-specific functions in addition to the pipetting programs. The Transferpette® electronic, for example, offers a program to simplify and speed up the calibration of the instrument as well as a battery refresh function.
    Mixing of Samples
    Program for mixing of liquids. The sample is repeatedly aspirated and discharged, and the number of mixing cycles is displayed.
    What does 'reverse' mean?
    A reversal of the stops used to measure a volume. Works with mechanical pipettes as follows: To aspirate the reagent, press the pipetting button down to the second stop and let it slide all the way back. Then press down just to the first stop to discharge the set volume.
    Program for mixing of liquids Reverse Pipetting
    Program specially designed for the pipetting of liquids with a high viscosity, high vapor pressure or foamy media. For a set volume, the blow-out volume is aspirated additionally. This volume remains in the tip after delivery to prevent undefined running out, splashing, or the formation of foam or bubbles.
    Pipetting with Electrophoresis
    Program for loading of electrophoresis gels. The required sample volume is aspirated. During discharge, the volume being dispensed is tracked continuously, allowing the user to stop discharge to avoid over-filling sample wells. The pipette records the exact volume dispensed to ensure accuracy of sample mass calculations. GEL mode may also be used for microtitrations.
    Dispensing
    A program for the dispensing of liquids in a series of equal aliquots. A volume that has been aspirated is dispensed in steps.

    Pipetting with positive-displacement pipettes

    Positive-displacement pipettes are the ideal alternative for difficult applications where air interface pipettes reach their physical limits. They are well suited even for media of very high or low viscosity, high vapor pressure, or a tendency to foam.

    Functional principle

    In contrast with air interface pipettes, the positive-displacement piston is in direct contact with the pipetted liquid. The piston wipes the walls of the tips/capillaries completely clean – literally to the last drop which can be observed leaving the tip orifice. This principle always provides reproducible results, regardless of the physical properties of the liquid. There is no need to discard tips or capillaries after each pipetting operation, since the minimal residual wetting is negligible for most applications. If carry-over is a concern, such as with infectious or radioactive media, an air interface pipette with disposable tips should be preferred.

    Benefits

    Highest accuracy and speedy operation. The tips or capillaries are reusable. No need for reading a meniscus for pipetting.

    Pipetting with positive-displacement pipettes

    e.g., Transferpettor by BRAND®

    Pipetting with positive-displacement pipettes

    Range of applicationRange of applicationRange of application

    Volume setting
    Select desired volume by turning the volume setting knob.
    Aspirate reagent
    Press piston to the stop. Immerse tip into reagent and slowly let the piston return to aspirate reagent.
    Discharge reagent
    Place the capillary/tip against the vessel wall and press the pipetting button down a second time to the stop. Positive displacement pipettes have no blow-out!

    Operation (similar to air interface pipettes)

    Dispensing with repetitive pipettes

    The distribution of liquids is one of the most important and common activities in medical, pharmaceutical and biological laboratories. The most common techniques are pipetting and dispensing. Dispensing refers to the repeated discharge of identical quantities of liquid. The dispensers described in this chapter eliminate the need for repeated intake after each step – a major time-saving compared to pipetting. Since dispensing is such a common technique, the ergonomic design of the devices plays an essential role. Dispensing tasks in the laboratory are rarely handled by fully automatic systems requiring no manual intervention. Generally, repetitive pipettes are used for these routine jobs.

    Types of repetitive pipettes:

    • Manual repetitive pipettes
    • Motorized electronic repetitive pipettes

    Functional principle

    With manual repetitive pipettes, the volume delivered in each step results from the length of the stroke, defined by the number of steps on a toothed rack, and the size of the tip. Therefore, only a limited number of defined dispensing steps is available. No intermediate volumes can be selected. A main advantage of these devices is their robustness; their drawback is their often fatiguing operation. Repetitive pipettes work on the proven positive-displacement principle. Therefore, even difficult media with high vapor pressure, high viscosity or a tendency to foam pose no problem to the repetitive pipettes. According to volume range, the repetitive pipette can be fitted with PD-Tips of different sizes.

    Functional principle

    Manual repetitive pipette, e.g., HandyStep® by BRAND®

    Manual repetitive pipette Manual repetitive pipette The repetitive pipette simplifies serial pipetting by taking up a medium once and then delivering it step by step. With one filling, up to 49 steps between 2 μL and 5 mL can be dispensed, depending on the size of the PD-Tip. The volumes and number of steps are a combined result of the setting of the volume selector key (1-5) and the size of the tip used. Positive-displacement tips (PD-Tips) from BRAND® are available in 10 different sizes, sterile or non-sterile. Compatible tips of other manufacturers may also be used.

    Available combinations with positive-displacement tips (PD-Tips) of different sizes from BRAND®

    Steps and volume ranges

    Available combinations with positive-displacement tips

    Ergonomics and design

    Repetitive working with hand-operated appliances can lead to a variety of muscular ailments which may particularly affect the neck, shoulders, arms and thumb. Fatigue-free operation is therefore a crucial requirement for repetitive pipettes, since they are used almost exclusively for serial dispensing. Ergonomic design is indispensable for the stress-free performance of extended pipetting operations in the same working position.

    Motorized electronic repetitive pipettes

    Functional principle Functional principle Intake and discharge are controlled by a single key. The piston inside the tips is driven by a motor, with a microprocessor controlling the volume and number of steps. The ergonomic design results in fatigue-free operation. The piston wipes the walls of the tips completely clean, providing precisely reproducible results without the influences of an air interface. The positive-displacement tips allow the dispensing of media of high density, high vapor pressure or volatility, or with a tendency to foam.
    Electronic repetitive pipettes In contrast to manual repetitive pipettes which only permit a limited number of volume settings, the electronic repetitive pipettes allow the continuous selection of intermediate volumes, such as 1.01 mL.

    Available working modes

    Materials