Pipetting may be one of the first things that you learn in the laboratory, but it is not as simple as it seems!
It requires a lot of practice to master this tool and manage to get all the volumes correctly even with difficult sample types. In this second part, we will discuss the two most common techniques: forward and reverse pipetting.
This technique is the most common one and could be used in almost every occasion. It is recommended for aqueous solutions, like buffers or salt solutions, volatile compounds like methanol, nucleotide solutions, acids and alkalis, and even radioactive compounds!
In this case, you will press to the first stop, aspire all the liquid by going back to the resting position and then releasing by pressing until the second stop. This way you will empty the tip completely.
This less used technique is very useful with some specific type of samples. It increases the accuracy of the volume taken of liquids that show high viscosity or foaming properties. It is so recommended for protein and nucleic solutions, oily solutions like glycerol and surfactant mixes like Tween. It could also be used for body fluids like whole blood or serum if high accuracy is required.
To perform this kind of liquid aspiration, you will have to press until the second stop in the first place, introduce the pipette into the sample and release up to the resting point. To dispense the sample, only press until the first stop. An additional tip: do every step very gently and slowly!