Pipette Function & Applications
Pipettes are used for the physical transfer of fluids. Such applications are necessary for many biological experiments, such as DNA & RNA extraction and cloning. There are a variety of pipette types, each optimized for the task at hand.
One of the most commonly used in the lab and operates with a piston mechanism to displace air. As the piston travels vertically through the airtight sleeve, a vacuum is generated, allowing for the target liquid around the pipette tip to move into the pipette. However, given these pipettes function through the use of air, the local environment (especially temperature) can cause imprecision, so be sure to calibrate pipettes frequently.
Air-displacement Pipettes range from 0.1 µl to 1000 µl, and come with four standardized tip sizes:
P10: 0.5 – 10 µl (white)
P20: 2 – 20 µl (yellow)
P200: 20 – 200 µl (yellow)
P1000: 200 – 1000 (blue)
Given the extensive use of air-displacement pipettes, they often come with a variety of channel types:
Single-channel pipettes – One of the most common forms pipettes come in, single channel pipettes only transfer one sample aliquot at a time.
Multichannel pipettes – Come in multiple formats, usually with 8 -, 12- or 16-channels. These pipettes can extract 8 – 16 aliquots and are very productive when working with plates or multiple samples.
Other Pipette Types
Electronic Pipettes – An automated form of single or multichannel pipettes.
Positive displacement pipette – similar to air-displacement, but contains a microsyringe and plunger which displaces the target liquid directly. Although not as common as air-displacement pipettes, positive displacement pipettes are useful for viscous substances such as DNA, or to prevent contamination.
Volumetric pipettes – More commonly known as bulb pipettes, they utilize a large bulb which when pressed, creates a vacuum within the pipette allowing for the target liquid to be drawn in. Usually, volumetric pipettes are used for creating solutions from a base stock, and come in volumes around 10 – 50 ml.
Graduated Pipettes – a macropipette with a graduated tube, signaling different volumes. Similar to bulb pipettes, graduated pipettes require a vacuum source.
Pasteur pipettes – plastic or glass tubes used with a bulb to transfer smaller amounts of liquid, with no specified volume.
Transfer pipettes – also known as Beral pipettes, are like Pasteur pipettes, but come with a built-in plastic bulb instead.