Pipette

A pipette is a device for measuring and transferring small volumes of liquid. Designs range from simple calibrated tubes to adjustable instruments that dispense liquid by controlled air displacement.

Air-displacement pipette: A pipette that moves liquid through a disposable tip by changing the air volume above it. Its piston-driven air cushion is the common mechanism in adjustable laboratory pipettes.
Volume: The amount of three-dimensional space occupied by a substance. A pipette's central measurement is the volume of liquid delivered.
Serial dilution: A sequence of dilutions in which each step uses the preceding diluted sample. Pipettes transfer precise aliquots at each step of the dilution series.
Burette: A graduated glass tube with a valve for dispensing measured liquid, especially in titrations. A burette releases liquid continuously through a stopcock rather than by pipette transfer.
Positive-displacement pipette: A pipette in which a piston contacts the liquid directly inside a capillary tip. Direct piston contact reduces errors with viscous, volatile, or foaming liquids.
Meniscus: The curved surface of a liquid where it meets a container or tube. Reading a glass pipette accurately requires aligning the meniscus with its mark.
Polymerase chain reaction: A laboratory method that amplifies selected DNA sequences through repeated thermal cycles. Small reagent volumes are pipetted into reaction mixtures before amplification.
Syringe: A piston-driven device that draws in or expels fluid through a nozzle or needle. A syringe can transfer liquid, but its common designs and uses differ from calibrated pipettes.
Volumetric pipette: A calibrated glass pipette designed to deliver one specified volume with high accuracy. Its fixed-volume design contrasts with adjustable pipettes.
Accuracy and precision: Accuracy is closeness to a true value; precision is closeness among repeated measurements. Pipette performance depends on both delivering the right volume and repeating it consistently.

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