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Forward pipetting is a technique to dispense a measured quantity of liquid by means of
In forward pipetting, an exactly set volume of liquid is aspired to the tip and then it is delivered to a new vessel. This is achieved by creating vacuum by means of the vertical travel of a metal or ceramic piston within an airtight sleeve. As the piston moves upward, driven by the depression of the plunger, a vacuum is created in the space left vacant by the piston. Air from the tip rises to fill the space left vacant, and the tip air is then replaced by the liquid, which is drawn up into the tip and thus available for transport and dispensing elsewhere.
When the pipette knob is pressed on an
File:Pipetting (2).jpg, User ready to dispense liquid present in pipette tip
File:Pipetting culture media.jpg, A scientist withdrawing pipette tip from liquid after dispensing
File:NHGRI researcher uses a pipette to remove DNA from a micro test tube.jpg , Research aspirating
Guide to pipettingWikilectures: Pipettors
Gilson websiteAndrew Alliance websiteThermo ScientificSocorexBiohitINTEGRA Biosciences
air displacement pipette
Piston-driven air displacement pipettes are a type of micropipette, which are tools to handle volumes of liquid in the microliter scale. They are more commonly used in biology and biochemistry, and less commonly in chemistry; the equipment is su ...
. The technique is mainly recommended for aqueous solutions, such as buffers, or diluted acids or alkalis. In case of solutions with a high viscosity
Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...
or a tendency to foam, reverse pipetting
Reverse pipetting is a technique to dispense a measured quantity of liquid by means of air displacement pipette. The technique is mainly recommended for solutions with a high viscosity or a tendency to foam: as it reduces the risk of splashing, fo ...
is more suitable.
How it works
In forward pipetting, an exactly set volume of liquid is aspired to the tip and then it is delivered to a new vessel. This is achieved by creating vacuum by means of the vertical travel of a metal or ceramic piston within an airtight sleeve. As the piston moves upward, driven by the depression of the plunger, a vacuum is created in the space left vacant by the piston. Air from the tip rises to fill the space left vacant, and the tip air is then replaced by the liquid, which is drawn up into the tip and thus available for transport and dispensing elsewhere.
When the pipette knob is pressed on an air displacement pipette
Piston-driven air displacement pipettes are a type of micropipette, which are tools to handle volumes of liquid in the microliter scale. They are more commonly used in biology and biochemistry, and less commonly in chemistry; the equipment is su ...
, the piston inside the instrument moves down to let air out. Air is displaced by the piston. The volume of air displaced is equivalent to the volume of liquid aspirated.
These pipettes are capable of being very precise and accurate. However, since they rely on air displacement, they are subject to inaccuracies caused by the changing environment, particularly temperature and user technique. For these reasons, this equipment must be carefully maintained and calibrated, and users must be trained to exercise correct and consistent technique.
Alternative solutions to improve reproducibility and accuracy of manual pipetting operations are based on liquid handling robots capable of handling air displacement pipettes.
Technique
Forward pipetting
The standard forward pipetting technique is used to dispense and mix a sample or reagent into another liquidPipetting of heterogeneous samples
When prerinsing tip is not possible and the full sample must be dispensed for correct analysis, the following alternative of forward pipetting is preferred. Indeed this technique is used for pipetting heterogeneous samples, such asblood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells.
Blood is com ...
or serum.
References
DNA
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
sample from microtube
File:Micropipettes.jpg , Set of air displacement pipette
Piston-driven air displacement pipettes are a type of micropipette, which are tools to handle volumes of liquid in the microliter scale. They are more commonly used in biology and biochemistry, and less commonly in chemistry; the equipment is su ...
s (Gilson and Eppendorf)
File:Monoclonal antibodies (8).jpg , Forward pipetting into 24-well plate
File:Pipette2.jpg , Man pipetting viscous solution
File:Pipette tips (1).JPG , Box of pipette tips in SBS format (Starlab)
File:Multichannel pipette.jpg , Multichannel pipette (Micronic)
Sources
Guide to pipetting
External links
Gilson website
See also
* Automated pipetting system * Liquid handling robot *Pipette
A pipette (sometimes spelled as pipet) is a type of laboratory tool commonly used in chemistry and biology to transport a measured volume of liquid, often as a media dispenser. Pipettes come in several designs for various purposes with differing ...
*Air displacement pipette
Piston-driven air displacement pipettes are a type of micropipette, which are tools to handle volumes of liquid in the microliter scale. They are more commonly used in biology and biochemistry, and less commonly in chemistry; the equipment is su ...
*Reverse pipetting
Reverse pipetting is a technique to dispense a measured quantity of liquid by means of air displacement pipette. The technique is mainly recommended for solutions with a high viscosity or a tendency to foam: as it reduces the risk of splashing, fo ...
{{Laboratory equipment
Laboratory equipment