A simple, critical, instrument in labs across the world, a pipette transports a measured volume of liquid safely and accurately. Pipettes can be as simple as plastic tubes and as complex as precise electronic devices. They generally have a single channel, eight (8) channels, or twelve (12) channels. Dr. Heinrich Schnitger, from Marburg, Germany, invented the first micropipette in 1957. This model measured and transported a fixed amount.
Later, the co-founder of biotechnology company Eppendorf, Dr. Heinrich Netheler, inherited the rights and initiated the global and general use of micropipettes in labs. In 1972, Warren Gilson and Henry Lardy, of Wisconsin, developed the first adjustable micropipette. Micropipettes dispense between one (1) and one thousand (1000) μl (microliters), while macropipettes dispense greater volume. Most pipettes work by creating a partial vacuum above the liquid-holding chamber, or the tip, and selectively releasing this vacuum to draw up and dispense liquid.
The Air Displacement Pipette
Air displacement micropipettes deliver a measured volume of liquid, depending on size. Additionally, they require disposable tips that come in contact with the fluid and operate using a piston-driven air displacement. The vertical movement of a metal or ceramic piston within an airtight tube creates a vacuum. The pipetting liquid around the tip moves into the vacuum and can then be moved and dispensed as needed.
These pipettes have the capability of precise and accurate measurement, but since they rely on air displacement, changing environmental conditions, especially air temperature and user technique, can introduce inaccuracy. Because of this, such equipment requires regular maintenance and calibration. End users should receive training to properly use correct and consistent technique.
The Positive Displacement Pipette
Similar in function to air displacement pipettes, positive displacement pipettes see less common use. Generally, users deploy these pipettes to avoid contamination and to handle volatile or viscous substances, or extremely small volumes, like DNA. The main difference comes in the disposable tip, a microsyringe made up of a capillary and a piston which directly displaces the liquid.
Volumetric pipettes, otherwise known as bulb pipettes, have a large bulb with a long narrow portion above a single graduation mark. This mark serves as the calibration point for a single volume, similar to a volumetric flask.
A single piece of plastic forms transfer pipettes, also known as beral pipettes. In beral pipettes, the bulb sometimes serves as the liquid holding vessel.
Electronic pipettes were developed to improve ergonomics of pipettes by reducing the necessary force to operate them. A small electric motor powered by an internal battery replaces manual piston movement. Where manual pipettes require a movement of the thumb, electronic pipettes operate by the push of a button. Users employ a digital display on the unit to program settings such as volume.
Modern advancements in science and technology changed the look and operation of pipettes over the years, but not their main purposes. Pipettes, to this day, move a liquid from one place to another accurately and safely.