Types of pipettes

There are two main sorts of pipettes used for accurately dispensing volumes of solutions: volumetric and graduated. Pipettes are manufactured in a range of styles, and it is important to understand the differences.

Graduated vs Volumetric

Volumetric pipptettes are designed to accuratley measure a single fixed volume and thus only have a single graduation mark and usually feature a bulb half way up the pippette. Graduated pipetes are slightly less acurate than a volumetric pippette however are designed to meaure multiple volumes and thus have multiple graduations on.

Mohr (drain out) vs Serological (blow out) graduated pipettes

Pipettes may be labelled ‘BLOWOUT’ which indicates that every drop of liquid in the pipette is counted as part of the volume, meaning that the last drop needs to be ‘blown out’ of the pipette to ensure the correct volume is measured. Non-blowout pipettes differ in that the final drop of liquid that remains in a pipette is accounted for with the graduations and should not be forced out of the pipette when measuring volumes TAPING SURFACE . Drain out pipettes are often marked with a zero at the start of their conical end where as blow out do not display zero marks. 

Volume graduations

Pipettes vary with the graduations as to whether they run from 0 to the pipette volume from the end of the pipette to the top or vice-versa. To take a 5 mL pipette as an example, on pipettes that start with 0 mL at the tip (top image), if you wanted to measure 3 mL of liquid, you would draw the liquid to the 3 mL mark which would then dispense the correct volume. Whereas for a 5 mL pipette where the tip starts at 5 mL (bottom image) you would calculate the difference, therefore you would fill the pipette to the 2 mL mark in order to dispense 3 mL.