Pipette calibration services: what calibration of pipette testing must report, how pipette calibrations and on-site pipette calibration services are scheduled, and what an accredited certificate has to state

What a proper calibration reports

1. Multiple volumes, multiple replicates. Testing at several volumes across the instrument's range, with several replicates at each, is what reveals both systematic error and imprecision. A single volume tested once is a check that the instrument aspirates, not a calibration.
2. As-found before as-left. The as-found result is the one that matters, because it tells you how the instrument was performing during the work you already did. A service that adjusts first and reports only the final state has destroyed the information you were paying for.
3. Stated acceptance criteria. The certificate should state the limits applied and where they came from, whether the international standard's values or your own tighter internal specification. Limits that are not stated cannot be checked and cannot be compared between providers.
4. Conditions and the balance. Gravimetric calibration depends on temperature, humidity, barometric pressure and the balance used, and a credible certificate records them. This is also why a bench calibration in your own laboratory can be more representative than one performed at a service centre.
5. Accreditation, and when you need it. An accredited certificate carries the weight of a third party assessment of the provider's competence and traceability. Regulated and accredited laboratories generally need it; a research laboratory frequently does not and can buy a competent unaccredited service far more cheaply.

Setting the interval

Interval follows use and consequence rather than the calendar. An instrument pipetting a validated assay many times a day earns a much shorter interval than one used occasionally for buffers, and the sensible arrangement is a formal external service on a fixed cycle with quick internal checks between.

The internal check is a gravimetric test at one or two volumes on an analytical balance, taking minutes. Laboratories that do it find worn seals and damaged tip cones long before the annual service would, which is the whole point.

On site or shipped away

On-site service calibrates the instrument in the environment it works in and avoids a fleet being away for weeks. Shipped service can be cheaper per instrument and needs enough spare instruments to keep working, which is a hidden cost rarely in the quotation.

Whichever you choose, ask what happens when an instrument fails: whether adjustment and parts are included, what the turnaround is, and whether a loan instrument is provided.

Common questions

What should a pipette calibration certificate show?

As-found and as-left results at several volumes with several replicates each, the mean and the variability at each volume, the acceptance limits applied and their source, and the ambient conditions and balance used.

How often should pipettes be calibrated?

Set the interval from use and from what depends on the result, with a formal external service on a fixed cycle and quick internal gravimetric checks between. Heavy or regulated use warrants a much shorter interval.

Do I need an accredited calibration?

Regulated and accredited laboratories generally do. A research laboratory often does not, and can buy a competent unaccredited service far more cheaply, provided the certificate still reports real numbers.

Is on-site calibration better?

It calibrates the instrument in the environment where it works and avoids long absences. Shipped service can cost less per instrument but needs spares to cover the gap, which is rarely priced in the quotation.

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