Pipette

A pipette, or pipet, is a type of laboratory tool commonly used in chemistry and biology to transport a measured volume of liquid, often as a media dispenser. 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. Many pipette types work by creating a partial vacuum above the liquid-holding chamber and selectively releasing this vacuum to draw up and dispense liquid. Measurement accuracy varies greatly depending on the instrument.

History The first simple pipettes were made of glass, such as Pasteur pipettes. Large pipettes continue to be made of glass; others are made of squeezable plastic for situations where an exact volume is not required.

During or prior to 1877, Joseph Lister (1827 – 1912) invented the first adjustable micropipette, consisting of a "pipette with a syringe" (photograph shown at right).

"...by means of this little syringe with a graduated disc and a piston rod in the form of a screw, graduated 2-100ths of a minim, by which means you can, with perfect precision, unit 1-100th of a minim, or 2-100ths, or any number you choose."

The micropipette was patented in 1957 by Dr Heinrich Schnitger (Marburg, Germany). The founder of the company Eppendorf, Dr. Heinrich Netheler, inherited the rights and started the commercial production of micropipettes in 1961. The modern adjustable micropipette is a Wisconsin invention developed through interactions among several people, primarily inventor Warren Gilson and Henry Lardy, a professor of biochemistry at the University of Wisconsin–Madison. In 1984, Mettler-Toledo Rainin introduced one of the first commercially available electronic pipettes, contributing to the adoption of electronically controlled liquid handling in laboratory workflows.

Nomenclature Although specific names exist for each type of pipette, in practice, any type can be referred to as a "pipette". Pipettes that dispense less than 1000 μL are sometimes distinguished as micropipettes. The terms "pipette" and "pipet" are used interchangeably despite minor historical differences in their usage.

Common pipettes

Air displacement micropipettes

Air displacement micropipettes are a type of adjustable micropipette that deliver a measured volume of liquid; depending on size, it could be between about 0.1 μL to 1,000 μL (1 mL). These pipettes require disposable tips that come in contact with the fluid. These pipettes operate by piston-driven air displacement. A vacuum is generated by the vertical travel of a metal or ceramic piston within an airtight sleeve. As the piston moves upward, driven by the depression of the plunger, a vacuum is created in the space left vacant by the piston. The liquid around the tip moves into this vacuum (along with the air in the tip) and can then be transported and released as necessary. These pipettes are capable of being very precise and accurate. However, since they rely on air displacement, they are subject to inaccuracies caused by the changing environment, particularly temperature and user technique. For these reasons, this equipment must be carefully maintained and calibrated, and users must be trained to exercise correct and consistent technique. The first verified adjustable air displacement micropipette was invented by Joseph Lister during or prior to 1877 (see History section above). The modern micropipette was patented in 1960 by Dr. Heinrich Schnitger in Marburg, Germany. Afterwards, the co-founder of the biotechnology company Eppendorf, Dr. Heinrich Netheler, inherited the rights and initiated the global and general use of micropipettes in labs. In 1972, the modern adjustable micropipette was invented at the University of Wisconsin-Madison by several people, primarily Warren Gilson and Henry Lardy. Types of air displacement pipettes include:

adjustable or fixed volume handled Single-channel, multi-channel or repeater conical tips or cylindrical tips standard or locking manual or electronic manufacturer Irrespective of brand or expense of pipette, every micropipette manufacturer recommends checking the calibration at least every six months, if used regularly. Companies in the drug or food industries are required to calibrate their pipettes quarterly (every three months). Schools which are conducting chemistry classes can have this process annually. Those studying forensics and research where a great deal of testing is commonplace will perform monthly calibrations.

Electronic pipette

To minimize the possible development of musculoskeletal disorders due to repetitive pipetting, electronic pipettes commonly replace the mechanical version.

Positive displacement pipette

These are similar to air displacement pipettes, but are less commonly used and are used to avoid contamination and for volatile or viscous substances at small volumes, such as DNA. The major difference is that the disposable tip is a microsyringe (plastic), composed of a capillary and a piston (movable inner part) which directly displaces the liquid.

Volumetric pipettes

Volumetric pipettes or bulb pipette allow the user to measure a volume of solution extremely precisely (precision of four significant figures). These pipettes have a large bulb with a long narrow portion above with a single graduation mark as it is calibrated for a single volume (like a volumetric flask). Typical volumes are 20, 50, and 100 mL. Volumetric pipettes are commonly used to make laboratory solutions from a base stock as well as prepare solutions for titration.

Graduated pipettes

Graduated pipettes are a type of macropipette consisting of a long tube with a series of graduations, as on a graduated cylinder or burette, to indicate different calibrated volumes. They also require a source of vacuum; in the early days of chemistry and biology, the mouth was used. The safety regulations included the statement: "Never pipette by mouth KCN, NH3, strong acids, bases and mercury salts". Some pipettes were manufactured with two bubbles between the mouth piece and the solution level line, to protect the chemist from accidental swallowing of the solution.

Pasteur pipette Pasteur pipettes are plastic or glass pipettes used to transfer small amounts of liquids, but are not graduated or calibrated for any particular volume. The bulb is separate from the pipette body. Pasteur pipettes are also called teat pipettes, droppers, eye droppers and chemical droppers.

Transfer pipettes

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