A pipette (sometimes called pipet) is a laboratory tool used to transfer a measured volume of liquid, generally as a media dispenser, in chemistry, biology, and medicine. Pipettes are available in a variety of designs and levels of accuracy and precision, ranging from simple single-piece glass pipettes to more complex adjustable or electronic pipettes. Many pipettes work by drawing up and dispensing liquid by establishing a partial vacuum above the liquid-holding chamber and selectively releasing this vacuum. The precision of measurements varies substantially depending on the equipment.
Air displacement micropipettes
Air displacement pipette Single-Channel Pipettes designed to handle 1–5ml and 100–1000µl with locking systemA 5,000 μl (5 ml) pipette, with the volume to be transferred indicated. 500 means that the amount transferred is 5,000 μl.A 1,000 μl (1 ml) pipette, with the volume to be transferred indicated.A variety of pipette tips
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. The four standard sizes of micropipettes correspond to four different disposable tip colors
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 micropipette was invented and 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 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
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.
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.