Pipette

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

Pipette

Clockwise from top left: various sizes of micropipettes; a graduated serological pipette attached to an electronic manual pipetter; two Pasteur pipettes.
Classification	Media dispenser
Uses	Volume measurement, liquid transfer
Used with	Plastic disposable tips Dispenser

Apipette(sometimes spelled aspipet) is a type of laboratory tool commonly used inchemistryandbiologyto transport a measured volume of liquid, often as amedia dispenser.Pipettes come in several designs for various purposes with differing levels ofaccuracy and precision,from single piece glass pipettes to more complex adjustable or electronic pipettes. Many pipette types work by creating apartial vacuumabove 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 in glass, such asPasteur pipettes.Large pipettes continue to be made in glass; others are made in squeezable plastic for situations where an exact volume is not required.

The first micropipette was patented in 1957 by DrHeinrich Schnitger(Marburg,Germany). The founder of the companyEppendorf,Dr. Heinrich Netheler, inherited the rights and started the commercial production of micropipettes in 1961.

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 theUniversity of Wisconsin–Madison.

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 1000μLare sometimes distinguished as micropipettes.

The terms "pipette" and "pipet" are used interchangeably despite minor historical differences in their usage.

Common pipettes

Air displacement micropipettes

Main article:Air displacement pipette

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

A 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 0.1μLto 1,000 μL (1 mL). These pipettes require disposable tips that come in contact with the fluid.

These pipettes operate bypiston-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 SchnitgerinMarburg,Germany. Afterwards, the co-founder of the biotechnology companyEppendorf,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
• 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 conductingchemistryclasses can have this process annually. Those studying forensics and research where a great deal of testing is commonplace will perform monthly calibrations.

Electronic pipette

Main article:Electronic pipettes

To minimize the possible development ofmusculoskeletal disordersdue to repetitive pipetting,electronic pipettescommonly replace the mechanical version.

Single-ChannelElectronic Pipettesdesigned to handle 0.5–10ml

VIAFLO electronic multichannel pipettes from INTEGRA Biosciences

Positive displacement pipette

Main article: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 asDNA.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.

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  Positive displacement pipette
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  Thechuckwhich will be used to move the plunger
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  An early pipette

Volumetric pipettes

Main article:Volumetric pipettes

Several sizes of volumetric pipette.

Volumetric pipettesorbulb pipetteallow 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 avolumetric 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 fortitration.

Graduated pipettes

Main article:Graduated pipette

Graduated pipettesare a type of macropipette consisting of a long tube with a series of graduations, as on agraduated cylinderorburette,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.

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

Pasteur pipette

Pasteur pipettes with rubber bulbs attached.

Pasteur pipettesare 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 calledteatpipettes,droppers,eye droppersandchemical droppers.

Transfer pipettes

A transfer pipette

Transfer pipettes,also known asBeral 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, andburettes.They are calibrated toISOvolumetric A grade standards. A glass or plastic pipette tube is used with a thumb-operated piston andPTFEseal 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.

Van Slyke pipette

The Van Slyke pipette, invented byDonald Dexter Van Slyke,is a graduated pipette commonly used inmedical technologywith serologic pipettes for volumetric analysis.

Ostwald–Folin pipette

The Ostwald–Folin pipette, developed byWilhelm Ostwaldand refined byOtto Folin,is a type of volumetric pipette used to measure viscous fluids such as whole blood or serum.

Winkler–Dennis gas combustion pipette

Combustion pipette

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

Glass micropipette

Carlsberg pipettes, glass micropipettes, named for the place for their invention and first use, The Carlsberg Laboratory, Physiology Department, Copenhagen, Denmark. Used with a mouthpiece for precision biochemical and physiological labwork. From the top: double constriction pipettes for 1 and 10 microlitre; single constriction pipettes for 200; 2,000; and 10,000 microlitre

Borosilicateglass micropipettepulled with a Flaming/Brown micropipette puller P-97

These are used to physically interact with microscopic samples, such as in the procedures ofmicroinjectionandpatch clamping.Most micropipettes are made ofborosilicate,aluminosilicateorquartzwith 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 amicromanipulator.

Microfluidic pipette

A recent introduction into the micropipette field integrates the versatility ofmicrofluidicsinto 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 frompolydimethylsiloxane(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 LabatChalmers University of Technologyin Sweden.

Extremely low volume pipettes

Azeptolitrepipette has been developed atBrookhaven 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 howcrystallizationtakes place.

Pipette aids

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;a tablet can interact in real-time with the pipette and guide a user through a protocol;and a pipette station can help to control the pipette tip immersion depth and improve ergonomics.

Robots

An example of mechanical pipettes manipulated by an anthropomorphic robot

Pipette robotsare capable of manipulating the pipettes as humans would do.

Calibration

Pipette recalibrationis an important consideration in laboratories using these devices. It is the act of determining the accuracy of a measuring device by comparison withNISTtraceable reference standards. 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.

Posture and injuries

A biochemist pipetting

Proper pipetting posture is the most important element in establishing good ergonomic work practices.During repetitive tasks such as pipetting, maintaining body positions that provide a maximum of strength with the least amount of muscular stress is important to minimize the risk of injury. A number of common pipetting techniques have been identified as potentially hazardous due to biomechanical stress factors. Recommendations for corrective pipetting actions, made by various US governmental agencies and ergonomics experts, are presented below.

Winged elbow pipetting

Technique: elevated, “winged elbow”. The average human arm weighs approximately 6% of the total body weight. Holding a pipette with the elbow extended (winged elbow) in a static position places the weight of the arm onto the neck and shoulder muscles and reduces blood flow, thereby causing stress and fatigue. Muscle strength is also substantially reduced as arm flexion is increased.

Corrective action: Position elbows as close to the body as possible, with arms and wrists extended in straight, neutral positions (handshake posture). Keep work items within easy reach to limit extension and elevation of arm. Arm/hand elevation should not exceed 12” from the worksurface.

Over rotated arm pipetting

Technique: Over-rotated forearm and wrist. Rotation of the forearm in a supinated position (palm up) and/or wrist flexion increases the fluid pressure in the carpal tunnel. This increased pressure can result in compression of soft tissues like nerves, tendons and blood vessels, causing numbness in the thumb and fingers.

Corrective action: Forearm rotation angle near 45° pronation (palm down) should be maintained to minimize carpal tunnel pressure during repetitive activity.

Clenched fist pipetting

Technique: Tight grip (clenched fist). Hand fatigue results from continuous contact between a hard object and sensitive tissues. This occurs when a firm grip is needed to hold a pipette, such as when jamming on a tip, and results in diminished hand strength.

Corrective action: Use pipettes with hooks or other attributes that allow a relaxed grip and/or alleviate need to constantly grip the pipette. This will reduce tension in the arm, wrist and hand.

Thumb plunger pipetting

Technique: Concentrated area of force (contact stress between a hard object and sensitive tissues). Some devices have plungers and buttons with limited surface areas, requiring a great deal of force to be expended by the thumb or other finger in a concentrated area.

Corrective action: Use pipettes with large contoured or rounded plungers and buttons. This will disperse the pressure used to operate the pipette across the entire surface of the thumb or finger, reducing contact pressure to acceptable levels.

Incorrect posture can have a strong impact on available strength arm strength pipetting

Technique: elevated arm. Muscle strength is substantially reduced when arm flexion is increased.

Corrective action: Keep work items within easy reach to limit extension and elevation of arm. Arm/hand elevation should also not exceed 12” from the worksurface.

Elbow strength pipetting

Technique: Elbow flexion or abduction. Arm strength diminishes as elbow posture is deviated from a 90° position.

Corrective action: Keep forearm and hand elevation within 12” of the worksurface, which will allow the elbow to remain near a 90° position.

Unlike traditional axial pipettes, ergonomic pipetting can affect posture and prevent common pipetting injuries such as carpal tunnel syndrome, tendinitis and other musculoskeletal disorders.To be "ergonomically correct" significant changes to traditional pipetting postures are essential, like:

minimizing forearm and wrist rotations, keeping a low arm and elbow height and relaxing the shoulders and upper arms.

A smart pipette stand that can control electronic pipettes

Pipette stand

Typically the pipettes are vertically stored on holder called pipette stands. In case of electronic pipettes, such stands can recharge their batteries. The most advanced pipette stands can directly control electronic pipettes.

Alternatives

An alternative technology, especially for transferring small volumes (micro and nano litre range) isacoustic droplet ejection.

External links

• Helpful Hints on the Use of a Volumetric Pipetby Oliver Seely