Laboratory Pipettes

For titrations and standard solutions, use a volumetric pipette. For measuring out varying amounts, choose a graduated or serological pipette. If you only need to move a few drops, a Pasteur pipette does the job at a fraction of the price.

Class A pipettes have tighter tolerances and are the choice for analytical and accredited work. Class B pipettes allow roughly double the error, which is fine for teaching labs and routine checks, and they cost less. Both are made in borosilicate glass.

Pick a pipette whose capacity is close to the volume you're measuring. Drawing 2ml with a 25ml graduated pipette is far less accurate than using a 2ml volumetric pipette. For volumes in the microlitre range, an adjustable micropipette is the right tool.

Every pipette needs a filler. Rubber bulbs suit volumetric and graduated glass pipettes, thumbwheel pumps are sized to fit particular pipettes, and micropipettes need tips that fit the model. Check the fit before a practical, not halfway through it.

A pipette measures and transfers a volume of liquid from one container to another. Depending on the type, that could be one exact volume for a titration, any volume up to its capacity, a few drops of stain, or a microlitre-sized dose into a sample tube.

The three you'll meet most are volumetric pipettes, which deliver one fixed volume; graduated or serological pipettes, which measure variable volumes; and Pasteur or transfer pipettes for moving drops. Research and clinical labs add adjustable micropipettes for microlitre work.

A dropper, or Pasteur pipette, moves liquid without measuring it. A measuring pipette is calibrated, so it delivers a known volume within a stated tolerance. If the amount affects your result, use a graduated or volumetric pipette rather than a dropper.

Hold the pipette upright and bring the mark to eye level. For clear liquids, the bottom of the curved surface, the meniscus, should sit exactly on the line. Let a volumetric pipette drain on its own, touch the tip to the inside of the flask, and don't blow out the last drop unless the pipette is marked for it.

Rinse them with distilled water straight after use, soak them in warm lab detergent, then rinse several times with distilled water. Before measuring, rinse the pipette twice with a little of the solution you're about to use. Store pipettes in a stand so the tips don't chip.