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Matching device to task

1. Choose by volume decade, not by maximum. Accuracy is worst at the bottom of any device's range. Cover the laboratory's real volumes with two or three ranges rather than one general purpose instrument used everywhere, and keep the routine volume near the middle.
2. Match the mechanism to the liquid. Air displacement suits aqueous liquids and fails on viscous, volatile and dense ones. Positive displacement handles those correctly. Using the wrong mechanism produces a systematic error nobody sees.
3. Choose plate devices by format, not channel count. Head geometry has to match the plate, including well spacing and depth. A head that will not reach the bottom of a deep well, or that fouls a skirt, is unusable whatever its channel count.
4. Add repeat dispensing where the protocol repeats. A repeater or a dispenser removes the aspirate and dispense cycle for a series of identical volumes, which cuts both time and variability. It is the cheapest automation in a laboratory.
5. Calibrate on a schedule and keep the certificates. Set the interval from usage and consequence, run a simple gravimetric check between formal calibrations, and file the certificates against the instrument identifier rather than in a drawer.

Ergonomics is a real specification

Repetitive pipetting causes injury, and the devices that reduce it, electronic plungers, light springs, repeat dispensers and controllers for large volumes, are also the ones that reduce variability. The two improvements come together.

Where a person pipettes for hours a week, treat the device choice as an ergonomic decision as much as a technical one, and rotate tasks.

The bench is a system

Devices, tips, reservoirs, plates and racks have to fit each other. A reservoir that a multichannel head cannot reach the bottom of wastes reagent; a tip that does not seal changes the volume.

Standardise the set once across the laboratory. Protocols then transfer between benches without silent substitutions.

Common questions

Graduated or micropipette?

A graduated glass or plastic pipette with a controller handles millilitre transfers where a small error is immaterial. A micropipette handles microlitre volumes where it is not. Using either outside its decade is the commonest source of avoidable error.

When is positive displacement required?

For viscous, volatile, dense and foaming liquids, where the air cushion in a standard pipette expands, contracts or lets liquid escape. The tips cost more and the measurement is correct.

Is a repeat dispenser worth it?

For any protocol that dispenses the same volume more than a handful of times, yes. It reduces both time and variability, and it is far cheaper than a liquid handling platform.

How often should devices be calibrated?

By use and consequence rather than by calendar alone, with an in house gravimetric check between formal calibrations to catch drift early.

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