The Complete Handbook of Pipettes

Chapter 1: Understanding Pipettes

A pipette, at its most fundamental level, is an instrument for transferring a measured volume of liquid. That is the simple definition, but the reality of its use is that it is the single most important factor in determining the validity of your experimental results. If you are measuring the concentration of a drug in a blood sample, the amplification of DNA, or the amount of reagent to add to a reaction, your final answer is only as good as the accuracy of the volume you pipetted. This chapter will dissect what a pipette actually is, how it performs its task, and why the nuances of its design and use have outsized consequences for your work and your bottom line.

Most people, when they think of a pipette, picture the classic "micropipette" — a long, slender, pistol-like instrument with a disposable plastic tip on the end. This is an air displacement pipette. It works on a simple principle borrowed from a syringe, but with a crucial twist. Inside the pipette is a piston, which is essentially a plunger. When you press the push button on top, the piston moves down. When you release the button, a spring pushes the piston back up. This creates a vacuum — a partial void — inside the shaft of the pipette. The vacuum sucks liquid up into the detached tip that is mounted on the end.

Here is the crucial detail: the piston never actually comes into contact with