What Are the Functions of a Graduated Pipette?

Functions of Pipettes

• Pipettes are used to measure and transfer liquids in a laboratory setting. Pipettes work much like a drinking straw, drawing in liquid with suction. Rubber bulbs or pump valves are often used to draw liquid into a pipette. There are three basic kinds of pipettes: micropipettes, volumetric pipettes and graduated pipettes.

Graduated Pipettes

• With a graduated pipette, one can measure various amounts of liquids. Each graduated pipette is marked with a series of lines that indicate the amount of liquid that will be transferred. This allows the technician or scientist to measure different amounts of chemicals with the same instrument. There are two types of graduated pipettes: mohr pipettes and serological pipettes.

Mohr Pipettes

• Mohr pipettes are graduated pipettes on which the measurement marks or graduations end well before the tip. The amount of liquid is measured between the lines of the pipette rather than from the lines to the tip. In other words, the amount of liquid dispensed is the difference between the two lines rather than a single measurement.

Serological Pipettes

• When a graduated pipette has measurement marks all the way to its tip, it is a serological pipette. The amount of liquid dispensed in a serological pipette is determined by the top line the liquid reaches in the pipette. These pipettes come in two basic types: blow-out and drain-out. With drain-out pipettes, the liquid is drawn in as one would draw water into a straw. The liquid is held in place by closing off the pipette with a finger or stopper. In order to transfer the liquid to a new container, one simply removes the stopper and allows the liquid to drain into the new container. A blow-out pipette has colored or etched rings around the top. Some of the liquid will drain out, but the remaining amount needs to be "blown" out of the tube. It is not acceptable laboratory practice to draw or release liquids by mouth as one would with a straw. Pipette fillers are instruments that can be used to draw and "blow out" liquids in a pipette. Pipette fillers include a simple rubber bulb, a triple-valve bulb, an electronic pipette filler and a hand-operated pump.