Third-party testing (revision 7)

Third-party testing is the analysis of a material by a laboratory that is independent of the supplier and of the manufacturer, commissioned by the purchaser and reported to the purchaser. It is distinguished from a supplier's own certificate of analysis not by the analytical methods used, which may be identical, but by who paid for the work and who receives the result.^[1]

The distinction matters because the incentive structure differs. A supplier commissioning analysis of its own material controls which sample is submitted, whether an unfavourable result is published, and how the result is described. A purchaser commissioning analysis of material already received controls none of those things but is testing a sample of unknown representativeness.^[2]

Independent testing is therefore evidence about a sample rather than about a lot, and about a lot rather than about a supplier. Treating a single favourable independent report as a general statement about an organisation is the commonest error made with these documents.^[2]

An independent report establishes, at most, the properties of the material that reached the laboratory. Whether those properties can be extended to the lot the material came from depends on how the sample was drawn, and whether they can be extended to the supplier depends on how many lots have been examined and over what period.^[1]

Three separate questions are involved and are routinely collapsed into one.

1. Is this sample what it claims to be? Answered by identity determination — mass confirmation against the calculated mass, ideally with sequence-level confirmation. A purity figure alone does not answer it.
2. How pure is this sample? Answered by chromatographic purity, which is an area-normalised figure and not a mass.
3. How much active substance is in the vial? Answered only by peptide content together with a water determination and a fill mass. Purity does not answer it.