Pipette - Use and Variations

Use and Variations

Pipettes are commonly used in molecular biology, analytical chemistry, and 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 pipette 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. 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. Larger capacity tubular pipettes, such as volumetric or graduated pipettes, are used by temporarily attaching a pipetting dispenser. Pipetting syringes typically handle volumes in the 0.5 mL to 25 mL range, for aliquot transfer and incremental dispensing in titrations, with a positive displacement method of operation.