Good Pipetting Technique - Simple Ways to Minimise Errors
May 20 2010 Read 16133 Times
As with many forms of instrumentation, a pipette will perform only as well as the operator’s technique allows. Even with a high quality, well calibrated pipette using the finest precision tips, variations in user operation can alter delivery volumes and introduce inaccuracies. As many complex laboratory methods rely on basic pipetting in the initial set up stages it is vital to get this critical step right from the beginning.
Good technique increases accuracy by 0.1% to 5% Inaccuracy in results because of poor pipetting technique can be as high as 5%, enough to compromise your experimental results. However, by following some basic
procedures that easily become routine practice, you can achieve consistent pipetting results all day every day.
PIPETTE AND VOLUME SETTING
Start by choosing the optimal pipette for your dispensing volume. Work in the 35% to 100% volume range, for best accuracy and precision. Make sure you are using a well fitting tip designed for that pipette. When setting the micrometer turn it one third revolution above desired volume and then dial-down to required volume setting.
When using a fresh pipette tip for the first time it is important to pre-rinse the tip at least twice before pipetting. This pre-rinsing provides identical contact surfaces for all aliquots. It also helps to neutralise capillary
effects in micro-volume pipettes and – important for macro-volume pipettes – it equalises the air temperature inside the pipette to the sample temperature. This is especially important when pipetting hot or cold liquids.
Figure 1 shows how pre-rinsing twice achieves maximum accuracy, most critical for lowest volumes.
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