Select forward or reverse pipetting based on the liquid
Depress the plunger to the first stop, immerse the tip into the liquid, and aspirate by releasing the plunger. Remove the pipette from the liquid and depress the plunger to the second stop to dispense the entire contents. Standard (or forward) mode pipetting yields better accuracy and precision than reverse mode for all but viscous or volatile liquids. Reverse mode often results in over-delivery. Hence, it’s recommended to evaluate the effect of possible over-delivery in the experiment and make adjustments if needed.
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In this experiment 200µL of viscous liquid (glycerol) was pipetted 10 times by using both forward and reverse pipetting techniques. The pipette used was adjusted for glycerol using forward pipetting. The chart describes the accuracy and precision obtained with both techniques.
Using the reverse method a smaller deviation between doses was observed and therefore reduced imprecision.
The reverse method gave bigger doses as the liquid column in the tip is taller and therefore the liquid amount above the dose presses a larger dose out.
