pipettes

Pipettes are precision instruments used to measure and transfer precise volumes of liquid in laboratory settings. They are designed to provide accurate and repeatable results while minimizing sample contamination. The main categories are volumetric pipettes and micropipettes, with micropipettes covering small volumes from about 0.5 to 1000 microliters for routine lab work. Pipettes are available in adjustable-volume models and fixed-volume variants, and in both air-displacement and positive-displacement designs.

Air-displacement pipettes in general use disposable plastic tips. They function by drawing air into a cylinder as the piston moves, creating a sample-liquid volume at the tip. Positive-displacement pipettes have a direct-contact piston that is used when dealing with viscous, volatile, or foaming liquids where air may cause inaccuracies. Tips must be attached securely; pre-wetting tips with the intended liquid can improve accuracy.

Operation: set the desired volume with a dial, attach a fresh tip, press the plunger to the first stop, immerse the tip into the liquid, release the plunger slowly to draw up the liquid, then depress to the second stop to dispense. For viscous liquids or air-sensitive samples, adopt reverse pipetting or cool-down, and ensure complete dispensing before removal.

Calibration and quality assurance: routine calibration is required to ensure accuracy and precision. Methods include gravimetric testing or manufacturer-defined checks, often following ISO 8655 standards. Calibration should be traceable to national standards, and results documented. Most labs schedule periodic verification and service.

Maintenance and handling: keep pipettes clean and dry; use compatible tips; store upright and with tips ejected; avoid immersion of the body except as recommended. Clean with mild detergent, rinse with deionized water, and periodically service seals and pistons.