How to Read a Peptide Certificate of Analysis (CoA)

A certificate of analysis (CoA) is the single most useful document when comparing research-peptide suppliers. It is also easy to misread. This checklist covers what to look for.

1. Is it batch-specific?

A useful CoA names a batch or lot number that matches the vial you will receive, plus a test date. A generic certificate with no batch number, or one dated years ago, tells you very little about the material you are buying.

2. Identity: mass spectrometry

Mass spectrometry (MS) confirms the molecule is what the label says. Check that:

• The observed mass is reported, not just the expected mass
• It matches the theoretical molecular weight within a small tolerance
• The salt or modified form is taken into account (acetylation, amidation, PEGylation and lipidation all change the mass)

HPLC alone cannot confirm identity. A pure sample of the wrong peptide still gives a clean HPLC trace.

3. Purity: HPLC

High-performance liquid chromatography (HPLC) separates the main peptide from impurities. Look for:

• A purity percentage (for example ≥98%) and the chromatogram itself, not just a number
• One dominant peak, with impurity peaks labelled or accounted for
• The detection wavelength and method, if stated

HPLC purity is relative: it tells you what share of the detected material is the target peptide, not how much peptide is in the vial.

4. Quantity: net peptide content

A "10 mg" vial contains the peptide plus counter-ions (such as acetate or TFA) and water. Net peptide content — sometimes measured by amino-acid analysis or nitrogen content — tells you how much actual peptide is present. Many CoAs leave this out. If a supplier provides it, that's a sign of thoroughness, and it makes price-per-mg comparisons more meaningful.

5. Who did the testing?

• In-house testing is common but harder to verify.
• Third-party testing should name the laboratory. You can contact the lab to confirm the report is genuine.

Red flags

• No batch number, or the same certificate used for every batch
• HPLC only, with no mass-spec data
• A purity figure with no chromatogram
• Signs of editing, mismatched fonts, or a lab that can't be identified
• An identical CoA appearing under different supplier names

How PeptideCompare treats CoAs

Suppliers can attach a CoA to each listing. Unless a listing is marked as staff-verified, PeptideCompare does not independently verify these documents. Always do your own checks. Our confidence page explains how documentation feeds into supplier reliability signals.

Summary

A good CoA is batch-specific, confirms identity by mass spec, shows an HPLC chromatogram, and ideally states net peptide content. Use it together with price per mg to compare suppliers fairly. Nothing here is for human or veterinary use.