Pipetting

Pipetting is the technique of measuring and transferring precise volumes of liquid using a pipette. Pipettes come in several types, including air-displacement micropipettes for small volumes (typically 1 μL to 1000 μL), positive-displacement pipettes for viscous or volatile liquids, and larger-volume devices such as serological or volumetric pipettes. Each pipette usually uses a disposable tip to prevent cross-contamination and to preserve accuracy.

Operation generally involves selecting a calibrated volume, attaching a disposable tip, pre-wetting the tip to improve accuracy, and using a controlled sequence to aspirate and dispense. The plunger is pressed to a first stop to draw liquid, released to the appropriate volume, and then the liquid is dispensed by pressing to the second stop in a smooth, vertical motion. Some protocols call for a final blow-out to ensure all liquid is expelled. Proper technique includes keeping the tip near the liquid surface, avoiding bubbles, and maintaining a consistent angle and speed.

Calibration and quality control are essential to ensure reliable results. Regular calibration and verification of pipette accuracy and precision are standard practices, often conducted via gravimetric or traceable methods. Factors such as liquid properties, temperature, tip condition, and procedural consistency influence performance. Manufacturers provide tolerances and maintenance guidelines, and routine servicing or replacement of worn parts is common.

Pipetting is foundational in many laboratories, supporting applications in molecular biology, biochemistry, clinical testing, and pharmaceutical development. Automation and robotic systems extend pipetting capabilities, particularly for high-throughput work, while adherence to standardized technique and safety practices helps minimize error and cross-contamination.