Pipette

This article is about the laboratory tool. For the band, see The Pipettes.

A selection of pipettes

A pipette, pipet, pipettor or chemical dropper is a laboratory tool commonly used in chemistry, biology and medicine to transport a measured volume of liquid. 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 style.

History

The first micropipette was patented in 1960 by Dr Hanns Schmitz (Marburg/ Germany). The founder of the company Eppendorf, Dr. Heinrich Netheler, inherited the rights and started the commercial production of micropipettes within the sixties. The 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.

Nomenclature

Although specific descriptive names exist for each type of pipette, in practice any type of pipette will merely be referred to as a "pipette" and the desired device will be obvious from context. Sometimes, pipettes that dispense between 1 and 1000 μl are distinguished as micropipettes, while macropipettes dispense greater volumes.

Common pippettes

Air displacement micropipettes

Single-Channel Pipettes designed to handle 1-5ml and 100-1000µl with locking system

A variety of pipette tips

Main article: Air displacement pipette

Air displacement micropipettes are a type of adjustable micropipette that measured volume between about 0.1 µl to 1000 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:

Pipette type	Volumes (uL)	Tip color
P10	0.5 – 10	white
P20	2 – 20	yellow
P200	20 – 200	yellow
P1000	200 – 1000	blue

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. Hanns Schmitz of 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.

Micropipettes brands include Gilson, ErgoOne, Eppendorf, Hamilton, Rainin, Drummond, BrandTech, Oxford, Hirschmann, Biohit, Labnet, Nichiryo, Gilson, Corning, VistaLab, Thermo, Jencons, Vertex, Handypett, and Pricisexx.

Several different type of air displacement pipettes exist:

• 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 micro pipette 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 plunger which directly displaces the liquid.

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

Volumetric pipettes

Main article: Volumetric pipettes

Several sizes of volumetric pipette.

Volumetric pipettes or bulb pipette allow the user to measure a volume of solution extremely accurately (accuracy 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 10, 25, and 50 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. Graduated pipettes commonly come in 5, 10, 25 and 50 mL volumes.

To avoid accidental ingestion of potentially harmful substances, a variety of propipetters have been developed, both entirely manual and electrically assisted:

• 
  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 bulb
• 
  An automatic propipetter adjusted by pressing the button and toggling the switch
• 
  An automatic propipetter adjusted by pulling and releasing the triggers

Originally pipettes were made of soda-lime glass, but currently many are made of borosilicate glass; disposable graduated pipettes are often made of polystyrene. Graduated pipettes are often graduated in one of two ways:

• Mohr, backward or drain-out pipettes have a 0 mL mark just above the end of the pipette. A volume is pulled into the pippette, sometimes to the maximum volume, then the needed volume is aliquoted out.
• serological, forward or blow-out pipettes have no 0ml mark as that corresponds to an empty pipette. The volume needed is pulled into the pipette and then dispensed.

Top: A Mohr, backward or drain-out pipette. Bottom: Serological, forward or blow-out pipette.

Historically, the accuracy of a graduated pipette was not as good as that of a volumetric pipette (accuracy of 3 significant fig); however, with improved manufacturing methods, the accuracies listed by the manufacturer can equal volumetric pipettes. Graduated pipettes have +/- tolerances that range from 0.6% to 0.4% of the nominal volume when measured at 20 °C (68 °F). Graduated pipettes are manufactured according to ISO specifications for accuracy and the arrangement of the graduations. A-grade pipettes are more accurate than B-grade pipettes.

Pasteur pipette

Pasteur pipettes

Pasteur pipettes are plastic or glass pipettes used to transfer small amounts of liquids, but are not graduated or calibrated for any particular volume Pateur pipettes are also called teat pipettes, droppers, eye droppers and chemical droppers.

Transfer pipettes

A transfer pipette

[[Transfer pipette]s, 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.

Specialized pipettes

Pipetting syringe

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 0.5mL and 25mL. This arrangement provides improvements in precision, handling safety, reliability, economy, and versatility. No disposable tips or pipetting aids are needed with the pipetting syringe.

Van Slyke Pipette

A graduated pipette commonly used in medical technology with serologic pipettes for volumetric analysis. Invented by Donald Dexter Van Slyke.

Ostwald-Folin Pipette

A special pipette used in measuring viscous fluid such as whole blood. Common in medical technology laboratory setups together with other pipettes. Invented by Friedrich Wilhelm Ostwald, a Baltic German Chemist and later refined by Otto Folin, an American Chemist.

Glass micropipette

Borosilicate glass micropipette pulled with a Flaming/Brown micropipette puller P-97

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.

Microfluidic pipette

A Microfluidic pipette, housed in a manifold holder. The colored solutions highlight the sample wells of the PDMS pipette.

A recent introduction into the micropipette field integrates the versatility of microfluidics into a positionable pipette platform. These are used to create a recirculation zone, allowing for constant control of a micrometer sized environment at the tip of the pipette. Currently these pipettes are made of polydimethylsiloxane (PDMS) which is molded from a physical master. Interfacing of these pipettes allows for multiple solutions to be loaded and switched on demand, along with concentration control and solution pulsing. Invented by Alar Ainla in Owe Orwar's group at Chalmers University of Technology in Sweden.

Extremely low volume pipettes

A zeptoliter 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.

Robots

An example of pipettes manipulated by an anthropomorphic robot

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

Calibration

Pipette recalibration is an important consideration in laboratories using these devices. It is the act of examining or adjusting the quality of being near to the true value of a measuring device by comparison with a standard. Pipette calibration is essential to ensure that the instrument is working according to expectations and as per the defined regimes or work protocols. Pipette calibration is considered to be a complex affair because it includes many elements of calibration procedure and several calibration protocol options as well as makes and models of pipettes to consider.

External links

• Helpful Hints on the Use of a Volumetric Pipet by Oliver Seely
• The History of the Pipette (YouTube video)