How to Read a Peptide COA

A Certificate of Analysis is the document that separates a characterized research compound from an unlabeled vial. Every figure on it is the output of a specific measurement, and knowing which measurement answers which question is most of the skill of reading one.

ON THIS PAGE

1. Identity and purity are different measurements
2. What to look for in the HPLC section
3. What a credible lab looks like
4. What is usually NOT on a peptide COA

Identity and purity are different measurements

HPLC measures purity as chromatographic data. The number a certificate reports, by standard practice rather than by any single rule, is the area of the target peak as a percentage of all peaks in the chromatogram. A figure like 99.1% purity by HPLC describes how much of what is in the vial is one substance. It does not by itself confirm WHICH substance that is. Identity confirmation comes from mass spectrometry, which measures molecular weight against the expected value for the sequence. The split is not this publication's invention: ICH Q6B, the harmonized guideline on specifications for biotechnological and biological products, carries identity and purity as separate specification categories, with identity resting on methods specific to the molecule's structure. A COA that reports both is answering both questions. A COA that reports one number with no method named is answering neither.

What to look for in the HPLC section

• The method: column type, mobile phase, and detection wavelength. Their presence signals a real analytical run rather than a copied template.
• A retention time and a visible chromatogram, not just a percentage.
• The lot number, matching the vial in hand. A COA belongs to a lot, not to a catalog, and that is regulation rather than convention: 21 CFR 211.84, the federal rule on testing incoming components, lets a manufacturer rely on a supplier's certificate only lot by lot, each certificate standing for one lot's analysis and no other.

What a credible lab looks like

The testing laboratory should be named and independently verifiable, and verifiable has two checkable meanings. The first is accreditation: laboratories accredited to ISO/IEC 17025 hold that status from accreditation bodies that sign the ILAC Mutual Recognition Arrangement, and ILAC publishes a directory of those signatories, so an accreditation claim traces to a public record instead of resting on faith. The second is a lookup portal: some independent labs in this market run report-verification pages of their own, among them public.janoshik.com and checkpeptide.com, where entering a report identifier returns the lab's own copy of the document. A COA whose lab can be reached by neither route deserves skepticism.

What is usually NOT on a peptide COA

Sterility, endotoxin, and microbial testing are separate analyses and are usually not included unless stated. ICH Q6B carries them apart from identity and purity in its scheme of specifications, and FDA maintains standalone guidance on endotoxin testing, the March 2026 edition of Pyrogen and Endotoxins Testing: Questions and Answers, a separate analysis with methods of its own. A supplier that says plainly what has and has not been tested is communicating more honestly than one that implies everything was.

Sources: ICH Q6B, Specifications: Test Procedures and Acceptance Criteria for Biotechnological/Biological Products, guideline PDF at database.ich.org, retrieved 2026-09-01. FDA, Pyrogen and Endotoxins Testing: Questions and Answers, March 2026 edition, at fda.gov, retrieved 2026-09-01. 21 CFR 211.84 at ecfr.gov, current as of 2026-08-31, retrieved 2026-09-01. ILAC Mutual Recognition Arrangement signatory directory at ilac.org, retrieved 2026-09-01.