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A selection of pipettes
A pipette (also called a pipet, pipettor or chemical dropper) is a laboratory instrument used to transport a measured volume of liquid.

Use and variations

Pipettes are commonly used in molecular biology as well as medical tests. 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 pipettes types work by creating a partial vacuum above the liquid-holding chamber and selectively releasing this vacuum to draw up and dispense liquid.

Pipettes that dispense between 1 and 1000 μl are termed micropipettes, while macropipettes dispense a greater volume of liquid. Two types of micropipettes are generally used: air-displacement pipettes and positive-displacement pipettes. In particular, piston-driven air-displacement pipettes are micropipettes which dispense an adjustable volume of liquid from a disposable tip. The pipette body contains a plunger, which provides the suction to pull liquid into the tip when the piston is compressed and released. The maximum displacement of the plunger is set by a dial on the pipette body, allowing the delivery volume to be changed.Whereas for larger volumes cylindrical pipettes, such as volumetric or graduated pipettes are used and driven by a pipette aid.

Piston-driven air displacement pipettes

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


These pipettes are the most precise and accurate type of pipette, they 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. Air from the tip rises to fill the space left vacant, and the tip air is then replaced by the liquid, which is drawn up into the tip and thus available for transport and dispensing elsewhere.These micropipette were invented at the University of Wisconsin-Madison in 1972 by several people , primarily inventor Warren Gilson and Henry Lardy, hence the biggest producer is the original company called Gilson Inc., as a result they are colloquially refered to as Gilsons [15627] [15628].



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 elecronic
  • manufacturer


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.Image:Positive displacement.jpg| positive displacement pipetteImage:Pos pipette showing grappler.jpg| the chuck which will be used to move the plungerImage:early pipette.jpg|an early pipette

Vacuum assisted pipette

serological pipettes are used for large volumes and for sterile work, but require a pipette aid


Non-piston driven vacuum assisted pipettes are hollow narrow cylinders which work like a straw and require the use of some kind of additional suction device.Originally pipettes were made of pyrex glass, but currently are made of polystyrene. It is more commonly used in chemistry, with aqueous solutions. There are two types. One type, the volumetric pipette, has generally a large bulge with a long narrow portion above with a mark as it is calibrated for a single volume. Typical volumes are 10, 25, and 50 mL. Alternatively, graduated pipettes are straight-walled, and graduated for different volumes such as 5 mL in 0.5 mL increments. The single volume pipette is usually more accurate, with an error of ± 0.1 or 0.2 mL.

The pipette is filled by dipping the tip in the volume to be measured, and drawing up the liquid with a pipette filler past the inscribed mark. The volume is then set by releasing the vacuum using the pipette filler or a damp finger. While moving the pipette to the receiving vessel, care must be taken not to shake the pipette because the column of fluid may "bounce".

Volumetric pipettes

Volumetric pipettes allow the user to measure a volume of solution extremely accurately and then add it to something else. They are commonly used to make laboratory solutions from a base stock as well as prepare solutions for titration. They are typically marked to indicate one single volume in a particular size pipette (as are volumetric flasks). Many different sizes are available.

Graduated pipettes

Graduated pipettes use a series of marked lines (as on a graduated cylinder) to indicate different calibrated volumes. These also come in a variety of sizes. These are used much like a burette, in that the volume is found by calculating the difference of the liquid level before and after liquid is dispensed. Typically the precision of a graduated pipette is not as great as that of a volumetric pipette.Two types of graduated pipettes exist:
  • Mohr pipettes or drain-out pipettes have a 0ml mark before the start of the conical end, which is a dead volume.
  • serological or blow-out pipettes have no 0ml mark as that corresponds to an empty pipette.


Pipette aids

Various methods exist to handle the liquids inside a pipette. Before the advent of more sophisticated pipette aids, it was common practice to "mouth pipette" i.e. to aspirate fluid into the pipette by applying suction with one's mouth. the main three types of pipette aid are the bulb filler, pipette pump and the electronic controller or helper.Image:Bulb controller.jpg|bulb filler are the simplest cylindrical pipette controllers, where valves are opened or closed by squeezing the rubberImage:Manual controller.jpg|pipette pumps allow a more accurate handling of the volumes inside a cylindrical pipetteImage:Electronic controller.jpg|electronic controllers are expensive (200-300GB£) but allow an accurate and easy handling of volumes inside a cylindrical pipette

Pipette accessories

  • Pipette fillers are used to fill the pipette easily, avoiding the need for mouth pipetting.
  • Pipette helpers are battery-operated and are designed to be used with disposable pipette tubes. These pipettes cannot be calibrated and their accuracy is determined by that of the printed graduations on the disposable tubes.
  • Light-guided pipetting systems are pipetting accessories which are computer based. They utilize flat screen LCD monitors or LED arrays to light up source and destination wells in microplates or vials for accurate well to well pipetting. Some of these systems use text to speech to alert the operator during plate or volume changes when pipetting lab protocols.
  • Pipette tips. The pipettors and injection molded plastic disposable tips form together a reliable pipetting system. It is recommended to use original manufacturers tips to guarantee the precision and accuracy of the pipettes. The precision-made pipettor tips provide excellent reproducibility and accuracy. Pipettor tips are available in autoclavable boxes, refills and bulk packaging. Non-sterile, pre-sterilized and filtered tips are usually available in single trays as RNase, DNase and endotoxin certified free.


Pasteur pipette

Dispensable pipettes.
Pasteur pipettes, also known as droppers, are plastic or glass pipettes used to transfer small amounts of liquids, but are not graduated or calibrated for any particular volume. Transfer pipettes, also known as Beral pipettes, are similar to Pasteur pipettes. However, they are made from a single piece of plastic and their bulb can serve as the liquid-holding chamber.
A commercial variant of the pasteur pipette is the dispensable pipettes which are often made of plastic and intended to be used to administer medicine into the eye or ear of a patient (see image).

The smallest pipette

A zeptoliter pipette has been developed at Brookhaven National Laboratorymarker. 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.

References



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