Sizes & Uses of Pipettes

A pipette is a slender, graduated tube used in a laboratory for measuring and transferring quantities of liquids from one container to another. German pharmacist, Karl Friedrich Mohr, developed the calibrated pipette to enable specific amounts of liquids to be transferred. Kimble Glass manufactured his pipettes in New Jersey from 1920, as reported by the Smithsonian National Museum of American History. As of 2011, there are several different types of pipettes in a range of sizes and shapes, each measuring a variety of liquid volume for many scientific applications.

Micropipettors

• Used to transfer small amounts of liquids (under 1 ml), micropipettors have a scale of measurement on their outer casing in increments of 1000 microliters. There are three subtypes of micropipettors catering to different volumes of liquid: the P20 for volumes of 0.5 to 20 microliters, the P200 for volumes of between 20 and 200 microliters and the P1000 for volumes of 200 to 1000 microliters, according to the Davidson College Biology Department.

Volumetric Pipettes

• Volumetric or "TD" (to deliver) pipettes also come in a range of sizes, but are generally larger than micropipettes. They are unique in that each one delivers a specific quantity of a substance quickly and accurately. The liquid sample is sucked through the narrow glass tube into a centrally located glass "bulb." Each bulb has one volume printed on the glass exterior, such as 10 ml or 25 ml. Interestingly, the tiny amount of liquid left inside the tip after dispensing means the procedure has been accurate. If that tiny amount is ejected, too much liquid has been transferred, as explained by the Green River Community College.

Graduated Pipettes

• Graduated or "serological" pipettes are the opposite of volumetric pipettes because they can measure different amounts of a sample rather than just one amount. This reduced specificity does not mean they are drastically less accurate, although user precision is always a factor in non-digital analytics. This type of pipette can be made of glass or plastic and measures volumes of between 1 ml and 10 ml. A graduated pipette can be filled from the top using a pipette pump, which has a manual plunger and a simple wheel mechanism.

Automatic Pipettes

• Specifically designed to transfer liquid, automatic pipettes can be adjusted to accept different amounts of the sample. They have a bulb shape, like a volumetric pipette, but also they have a plunger, which is unique to this type of pipette, giving them the added function of a syringe, but with a much higher accuracy for much smaller amounts of liquid, often less than 5 ml, according to the Mountain Empire Community College.