A pipette is a laboratory instrument designed to accurately transfer specific volumes of liquid, typically measured in microlitres or millilitres.
Design and Operation
Pipettes provide controlled delivery of liquids by creating a vacuum and releasing fluid through a narrow tube. Air-displacement micropipettes are common in molecular biology and microbiology; they use a piston mechanism to aspirate liquid into a disposable tip and are calibrated to deliver (TD) the volume indicated. Users set the desired volume with a dial, depress the plunger to the first stop, submerge the tip just below the liquid surface, and slowly release the plunger to aspirate. Positive-displacement pipettes have a piston in direct contact with the liquid and are suitable for viscous or volatile solutions because they minimise evaporation and aerosols. Serological and volumetric pipettes are glass or plastic tubes with graduation marks; they are filled using a pipette pump or bulb and deliver volumes from 0.1 mL to tens of millilitres. Some are calibrated to contain (TC), meaning the entire volume must be expelled for accuracy. Pasteur pipettes are simple glass or plastic droppers for transferring approximate volumes. Correct pipetting technique involves pre-wetting the tip, holding the pipette vertically, and ejecting liquid smoothly to improve precision. Pipettes are regularly calibrated to maintain accuracy, and disposable tips prevent cross-contamination between samples.
Types and Laboratory Applications
Micropipettes are indispensable tools in modern microbiology, enabling precise handling of enzymes, nucleic acids and reagents in assays such as PCR, quantitative cultures and enzyme reactions. Adjustable air-displacement pipettes come in ranges such as 0.5–10 μl, 10‑100 μl and 100‑1000 μl; multi-channel versions accelerate microplate work. Serological pipettes are used to dispense media into culture dishes, transfer bacterial suspensions and aliquot reagents for fermentation experiments. Volumetric pipettes provide high accuracy for preparing standard solutions and dilutions in analytical chemistry. Glass Pasteur pipettes are useful for transferring small droplets during staining, inoculating agar plates or rinsing slides. Automatic pipetting robots combine precision pipettes with robotics to improve throughput and reproducibility in diagnostic laboratories. Choosing the appropriate type and practising proper technique are critical for reliable results across disciplines from microbiology and biochemistry to clinical diagnostics and pharmaceutical development.
Pipettes allow scientists to measure and transfer liquids with accuracy and precision across a broad volume range. Their various designs accommodate different sample properties and workflow requirements, ensuring reproducible experiments and sterile handling. Mastery of pipette selection and technique underpins quality laboratory practice.
Related Terms: Micropipette, Serological pipette, Volumetric pipette, Burette, Graduated cylinder