[Sam Tiktin]

A Certificate of Analysis (COA) is the single most useful document for evaluating a peptide supplier, but most of them are written for lab technicians, not for the person trying to decide whether a batch is trustworthy. This post walks through what a COA actually contains and how to read it critically.

What a COA Should Contain

A complete COA typically includes: the batch or lot number, manufacturing and testing dates, the molecular formula and theoretical molecular weight, the amino acid sequence, and the results of at least two independent analytical tests — usually reversed-phase HPLC for purity and mass spectrometry for identity confirmation, often alongside UV detection at 210–220 nm. Some COAs also include appearance, solubility, and endotoxin or microbial testing results, particularly for research applications where sterility matters.

Reading the HPLC Purity Result

HPLC (high-performance liquid chromatography) separates the components of a sample and reports the percentage of the total peak area attributable to the target peptide — this is the “purity” number most suppliers advertise. The number alone isn’t the whole story: a trustworthy COA includes the actual chromatogram, not just a stated percentage. A single clean, sharp peak with a flat baseline supports a high purity claim; a chromatogram with multiple secondary peaks or an elevated, noisy baseline can mean the batch contains meaningful impurities even if the headline number looks acceptable.

Reading the Mass Spectrometry Result

Mass spectrometry confirms identity rather than purity — it verifies the tested substance actually has the molecular weight expected for the peptide in question. Results are typically reported as an observed mass compared against the theoretical mass calculated from the amino acid sequence. Look for how closely the observed value matches the theoretical value, and be cautious of COAs that only report a wide tolerance band (for example, plus-or-minus a large percentage), since a wide tolerance can mask truncated sequences or amino acid substitutions that a tighter, modern LC-MS measurement would catch.

Common Red Flags

Watch for COAs with no visible chromatogram or spectrum (just a typed percentage), no batch number linking the document to the specific product received, testing dates that don’t align with any stated manufacturing timeline, or a generic COA that appears to be reused across multiple product listings. A COA that can’t be tied to the specific batch in hand isn’t verifying much of anything.

Related Reading

See our companion posts on HPLC vs Mass Spectrometry and what “99% purity” actually means for deeper detail on the two core tests. Browse COAs, Lab Testing & Documentation for related discussion.

Questions for Discussion

What details do you look for on a COA before trusting a purity claim? Has anyone had a supplier refuse to provide a batch-specific COA on request, and how did you handle that? What third-party testing options have members used to independently verify a supplier’s COA?

This post is educational information about interpreting laboratory documentation and does not constitute a recommendation to purchase or use any research compound.

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