Pipette

A pipette (sometimes spelled pipet) is a laboratory tool commonly used in chemistry, biology and medicine to transport a measured volume of liquid, often as a media dispenser. 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.The first simple pipettes were made in glass, such as Pasteur pipettes. Large pipettes continue to be made in glass; others are made in squeezable plastic for situations where an exact volume is not required.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.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 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:Positive displacement pipetteThe chuck which will be used to move the plungerAn early pipetteA person pipetting by mouth, now considered an unsafe practiceA manual propipetter adjusted by turning the wheel with the thumbA manual propipetter adjusted by squeezing the bulbAn automatic propipetter adjusted by pressing the button and toggling the switchAn automatic propipetter adjusted by pulling and releasing the triggersPipetting 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.Pipette recalibration is an important consideration in laboratories using these devices. It is the act of determining the accuracy of a measuring device by comparison with NIST traceable 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.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.Typically the pipettes are vertically stored on holder called pipette stands. In case of electronic pipettes, such stand can recharge their batteries. The most advance pipette stand can directly control electronic pipettes.