This article is about the laboratory instrument. For the band, see The Pipettes.
Sister project Look up pipette in
Wiktionary, the free dictionary.
A selection of pipettes
A pipette (also called a pipet, pipettor or chemical dropper) is a laboratory instrument used to transport a measured volume of liquid.
Pipettes are commonly used in chemistry and molecular biology research as well as medical tests. Pipettes come in several designs for various purposes with differing levels of accuracy and precision, from single piece glass pipettes to more complex adjustable or electronic pipettes. A pipette works by creating a vacuum above the liquid-holding chamber and selectively releasing this vacuum to draw up and dispense liquid.
Pipettes that dispense between 1 and 1000 μl are termed micropipettes, while macropipettes dispense a greater volume of liquid.
Volumetric pipettes allow the user to measure a volume of solution extremely accurately and then add it to something else. They are commonly used to make laboratory solutions from a base stock as well as prepare solutions for titration. They are typically marked to indicate one single volume in a particular size pipette (as are volumetric flasks). Many different sizes are available.
Graduated pipettes, also called Mohr pipettes, use a series of marked lines (as on a graduated cylinder) to indicate different calibrated volumes. These also come in a variety of sizes. These are used much like a burette, in that the volume is found by calculating the difference of the liquid level before and after liquid is dispensed. Typically the precision of a graduated pipette is not as great as that of a volumetric pipette.[citation needed]
A Pasteur pipette is not calibrated for any particular volume. Rather, it is essentially a large dropper, which can be used to remove liquid from one container and add it to another.
Variable volume air displacement pipettes are micropipettes which dispense an adjustable volume of liquid from a disposable tip. The pipette body contains a plunger, which provides the suction to pull liquid into the tip when the piston is compressed and released. The maximum displacement of the plunger is set by a dial on the pipette body, allowing the delivery volume to be changed.
A Beral pipette is a one-piece pipette, usually made from flexible soft plastic (polyethylene) that has a built-in bulb on the end.
All glass pipettes require the use of some kind of additional suction device, typically a pipette bulb, which is a rubber bulb which sucks the liquid into the pipette and also allows you to drain the pipette in a controlled fashion. Before this, it was common practice to "mouth pipette" i.e. to aspirate fluid into the pipette by applying suction with one's mouth.
The original pipette is made of glass. It is more commonly used in chemistry, with aqueous solutions. There are two types. One type, the volumetric pipette, has a large bulb, and is calibrated for a single volume. Typical volumes are 10, 25, and 50 mL. Alternatively, Mohr pipettes are straight-walled, and graduated for different volumes such as 5 mL in 0.5 mL increments. The single volume pipette is usually more accurate, with an error of ± 0.1 or 0.2 mL.
The pipette is filled by dipping the tip in the volume to be measured, and drawing up the liquid with a pipette filler past the inscribed mark. The volume is then set by releasing the vacuum using the pipette filler or a damp finger. While moving the pipette to the receiving vessel, care must be taken not to shake the pipette because the column of fluid may "bounce".
