ISO 8655 as a calibration framework

ISO 8655 is a framework a laboratory can point at when it talks about piston pipettes. It is not a charm that makes the pipette in a drawer accurate, and it is not a bench procedure you can skip writing. This glossary defines the words that framework actually uses, so a specification, a certificate, and a daily habit can refer to the same things. The handling those words assume is in accurate micropipetting technique.

Piston-operated volumetric apparatus

The series applies to piston-operated volumetric apparatus: instruments that deliver a selected volume by moving a piston. Pipettes are one part of that family. Part 1, ISO 8655-1:2022, sets terminology, general requirements, and user recommendations. Read that scope literally. It tells you how to speak and how a user should think about influences such as temperature, the tip, and technique. It does not measure your pipette. A photocopy of the title page in a drawer is not a calibration.

Part 2, ISO 8655-2:2022, is the pipette document. Its scope covers metrological requirements, maximum permissible errors, marking, and information for users, for air-displacement and positive-displacement pipettes, single-channel and multi-channel, complete with the selected tip. The numerical tolerances live in that standard and in the manufacturer specification. A laboratory compares its own gravimetric check with the specification it claims. This article will not invent or reprint an error table.

Other parts of the series describe how a reference measurement is made, including a gravimetric procedure. Follow those concepts at decision level: controlled water temperature, a balance that can see the error, repeats, and attention to evaporation. Do not paste a table you have not adopted into a notebook and call it compliance.

Systematic error and random error

Systematic error is the difference between the mean delivered volume and the volume you selected. If ten dispenses average low by the same amount, the centre of the result has moved. Causes in that class include a drifted adjustment, a tip family that does not seal the way the calibrated family did, a wrong mode, or a liquid temperature far from the condition of the test. The remedy is not to discard the odd points until the mean looks kind.

Random error is the width of those repeats. A wide scatter with a mean on target is a precision problem: unsteady rhythm, a loose tip on some strokes, bubbles, or a balance standing in a draught. Systematic and random error can both be outside the limits you claim, or only one of them. Reports that offer a single percentage without saying which error they mean are hard to act on. NIST's Office of Weights and Measures is one public home for the habit of separating those ideas. BIPM is where the international system those measurements are expressed in is maintained. Neither body calibrates your pipette by your reading this page.

Selected volume, nominal volume, and the tip

The nominal volume is the upper volume the pipette is built and marked to deliver, the name of its range. The selected volume is the volume you set for this dispense. Error limits are often widest, in relative terms, near the bottom of the range. Working at a small fraction of nominal volume and expecting the relative performance of the nominal point is a misreading of the framework. Choose a pipette whose selected volumes sit where its specification is still fit for the decision.

The selected tip is part of the apparatus. Tip fit is a metrology condition, not a purchasing footnote. A filter tip, a low-retention tip, and a plain tip can all be legitimate selections. They are not silent substitutions. User recommendations exist so that people pre-wet, hold the pipette in a defined way, and avoid treating a viscous liquid with an unexamined aqueous stroke. The recommendations guide a procedure. They do not replace the procedure your quality system signs.

What you do when a check disagrees with the claim

Write down the specification you claim before you weigh anything: manufacturer specification, a tighter internal limit, or the standard's maximum permissible errors at stated volumes. Then perform the check you actually have the balance and the skill to perform. An interim water check between formal calibrations is outlined in checking a pipette between calibrations. If the mean or the scatter falls outside the claim, the branch is to remove the pipette from quantitative service. Do not relabel the claim to match the bad week.

If the liquid is viscous, do not force the water framework to answer a glycerol question. Use the framework's separation of errors, check water to see that the piston is alive, then test the real liquid under the mode you will publish.

Safety and the limit of a standard

ISO 8655 does not assess biological risk. A calibrated pipette can still generate an aerosol. Containment is your institution's decision, informed by references such as the WHO laboratory biosafety manual where you use them. This glossary is research education. It is not accreditation, not a legal opinion, and not a diagnostic approval.

When you write a specification for a pipette that will be used in a hot, humid building, name the temperature at which you will check it. A framework written around controlled metrology rooms still applies, and the user recommendations already tell you that temperature is an influence. Put that sentence in your own procedure rather than assuming the room matches the printing city of the standard.

What an enquiry should cite

Say whether you need an instrument specified against the manufacturer tolerance, against ISO 8655-2 maximum permissible errors, or against a tighter internal limit, and at which volumes. Say air or positive displacement, channel count, and the tip family that must be part of the apparatus. Browse ranges in the scientific instruments catalogue and tips in the laboratory consumables catalogue. Send the cited document and the volumes with the quotation request.