Pipette

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 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.[5]

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.

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

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.

• Positive displacement pipette
• The chuck which will be used to move the plunger
• An early pipette

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 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.

• A person pipetting by mouth, now considered an unsafe practice
• A manual propipetter adjusted by turning the wheel with the thumb
• A manual propipetter adjusted by squeezing the valves marked E and S
• An automatic propipetter adjusted by pressing the button and toggling the switch
• An automatic propipetter adjusted by pulling and releasing the triggers

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, also known as Beral pipettes, are similar to Pasteur pipettes but are made from a single piece of plastic and their bulb can serve as the liquid-holding chamber.

Pipetting syringes are hand-held devices that combine the functions of volumetric (bulb) pipettes, graduated pipettes, and burettes. They are calibrated to ISO volumetric A grade standards. A glass or plastic pipette tube is used with a thumb-operated piston and PTFE seal which slides within the pipette in a positive displacement operation. Such a device can be used on a wide variety of fluids (aqueous, viscous, and volatile fluids; hydrocarbons; essential oils; and mixtures) in volumes between 0.5 mL and 25 mL. This arrangement provides improvements in precision, handling safety, reliability, economy, and versatility. No disposable tips or pipetting aids are needed with the pipetting syringe.

The Van Slyke pipette, invented by Donald Dexter Van Slyke, is a graduated pipette commonly used in medical technology with serologic pipettes for volumetric analysis.[6]

The Ostwald–Folin pipette, developed by Wilhelm Ostwald and refined by Otto Folin, is a type of volumetric pipette used to measure viscous fluids such as whole blood or serum.[7][8]

The Winkler–Dennis gas combustion pipette, developed by Clemens Winkler and refined by Louis Munroe Dennis, is an apparatus for the controlled reaction of liquids under a mild electric current and a supply of oxygen.[9]

These are used to physically interact with microscopic samples, such as in the procedures of microinjection and patch clamping. Most micropipettes are made of borosilicate, aluminosilicate or quartz with many types and sizes of glass tubing being available. Each of these compositions has unique properties which will determine suitable applications.

Glass micropipettes are fabricated in a micropipette puller and are typically used in a micromanipulator.

A recent introduction into the micropipette field integrates the versatility of microfluidics into a freely positionable pipette platform. At the tip of the device a localized flow zone is created, allowing for constant control of the nanolitre environment, directly in front of the pipette. The pipettes are made from polydimethylsiloxane (PDMS) which is formed using reactive injection molding. Interfacing of these pipettes using pneumatics enables multiple solutions to be loaded and switched on demand, with solution exchange times of 100ms.
Invented by Alar Ainla, currently situated in the Biophysical Technology Lab[10] at Chalmers University of Technology in Sweden.[11]

A zeptolitre pipette has been developed at Brookhaven National Laboratory. The pipette is made of a carbon shell, within which is an alloy of gold-germanium. The pipette was used to learn about how crystallization takes place.[12]

A variety of devices have been developed for safer, easier, and more efficient pipetting. For example, a motorized pipette controller can aid liquid aspiration or dispensing using volumetric pipettes or graduated pipettes;[13] a tablet can interact in real-time with the pipette and guide a user through a protocol;[14] and a pipette station can help to control the pipette tip immersion depth and improve ergonomics.[15]

Pipette robots are capable of manipulating the pipettes as humans would do.[16]