A Certificate of Analysis is the main piece of paper standing between you and an unverified claim about what's actually in a vial. Not all COAs carry the same weight — here's what to actually look at.
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Get my free report + free book →A Certificate of Analysis is testing documentation for a specific batch: what's in it, and how pure it is, based on lab analysis rather than a manufacturer's say-so. In a space with limited direct regulatory oversight, the COA is effectively the primary evidence a buyer has to evaluate a claim against.
High-performance liquid chromatography, HPLC, is the standard purity test — it separates the components of a sample and reports purity as the proportion of the main peptide peak relative to everything else detected. A useful COA reports the method behind that number, not just the percentage: the column type, the mobile phase, and the detection wavelength used, so the result can actually be evaluated rather than taken on faith. Mass spectrometry, particularly modern LC-MS/MS, verifies molecular weight and can confirm identity with very tight precision. It's worth watching the stated tolerance: a mass spec result reported only to plus-or-minus 0.1% can still be wide enough, on a peptide of a few thousand daltons, to mask a truncated sequence or an incorrect amino acid substitution. Tighter, more specific tolerances are a meaningfully better signal.
A handful of details separate a COA that supports its own claims from one that just asserts them: accreditation of the testing lab under a recognized standard like ISO 17025; a batch number on the COA that actually matches the label on the vial in hand; an actual chromatogram image rather than just a summary number; endotoxin results reported in the correct units for anything intended to be injectable; and a residual solvent panel covering compounds like TFA, acetonitrile, and DMF when those were used in synthesis or purification.
A few patterns are worth treating as red flags rather than minor omissions: no batch number, testing date, or identifiable lab anywhere on the document; a mass spec tolerance reported only at the loose plus-or-minus 0.1% level with nothing tighter; no way to independently confirm the testing lab actually exists and performed the work; a COA that comes only from the seller with no third-party accreditation behind it; and, most simply, a supplier who won't produce a COA at all when asked.
For how some of these same claims get overstated in marketing, see reconstitution myths.
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