Certificate of Analysis (COA)

A certificate of analysis accompanies a specific lot and reports, test by test, what was measured, against what specification, with what result. For a peptide the meaningful set is identity by mass spectrometry, purity by chromatography, net peptide content, water content, residual solvents, counterion content, and for injectables, endotoxin and sterility. A complete certificate also names the method behind each number, because a purity figure without a stated gradient, column and wavelength is not reproducible by anyone.

Within a regulated supply chain the certificate is a controlled document: it carries the lot number, the test dates, the specification limits agreed in the product specification, and an authorised signature accepting responsibility. The specification itself is justified by development and stability data and agreed with the regulator, not chosen by whoever is selling the material. Attached chromatograms and spectra let a reader verify the reported number rather than accept it.

What a certificate is good for is checking coverage. The tests that are absent tell you as much as the tests that passed. A document with a purity percentage and no net peptide content leaves the actual milligram content of the vial unaddressed; one with no endotoxin result says nothing about the risk that dominates parenteral use.

The persistent error is reading a certificate as independent verification when the seller produced or commissioned it and nothing in it traces to a named laboratory. Documents are trivially altered, and reused chromatograms, edited lot numbers and impossible decimal precision are common in the grey market. Even an honest certificate describes one lot at the moment of testing, in the manufacturer's hands, and says nothing about what shipping did to the vial afterwards.