COA

A Certificate of Analysis, almost always abbreviated COA, is a document issued by the manufacturer (or a contracted testing laboratory) that reports the results of the quality-control tests performed on a specific lot of a material. A COA is tied to a lot number: the same product name with a different lot number gets its own COA, because the tests were performed on that specific batch. For a synthetic peptide supplied as a research material, the COA is the primary document a researcher should use to evaluate whether the vial actually contains what the label claims and whether the impurity profile is acceptable for the intended downstream experiment.

What a peptide COA should contain

At minimum, a complete peptide COA reports: the product name and sequence (ideally with modifications and salt form explicit), the lot number and quantity, the manufacture and retest or expiry dates, an HPLC purity value with enough method detail to interpret it (column chemistry, gradient, detection wavelength), a mass-spectrometric identity confirmation (observed mass vs. theoretical mass), a net peptide content value if the material is a salt (typically measured by amino-acid analysis or by a nitrogen method, not assumed), a water content by Karl Fischer, a counterion content, a residual-solvents profile, and a bacterial endotoxin result when the material is intended for cell-based or animal-model research use. Many of these expectations are codified in USP General Chapter <1503> on synthetic peptide drug substances and in the FDA 2021 synthetic-peptide ANDA guidance (FDA 2021). Net-peptide content is particularly easy to miss: a vial labeled "10 mg" of a trifluoroacetate salt typically contains meaningfully less than 10 mg of peptide by mass, and quantitative experiments that do not correct for this introduce systematic error.

Signals that a COA is weak

Several patterns suggest that a COA is more branding than evidence. A "purity" value with no method attached, no gradient, and no chromatogram image; an identity statement that reads "confirmed by MS" without any observed mass; the absence of net-peptide content on a salt-form peptide; the absence of an endotoxin result for material being offered for research use; and identical COAs across multiple lot numbers (a copy-paste signal) are all reasons to weight the document lower. Peer-reviewed discussion of COA quality and supplier due diligence in the research-reagent market is summarized in Baker, Nature 2015 (NLM 25993940), a widely cited piece on reagent reproducibility.

How Open Assay uses COAs

Open Assay indexes the COAs that vendors publish or provide for the listings in its database, extracts the fields above, and displays them on the listing page. Missing fields are shown as missing rather than inferred. Listings with multiple lots over time allow a reader to see lot-to-lot variability in HPLC purity, net-peptide content, or endotoxin, which is often more informative than any single COA in isolation.