Reading a peptide COA: the buyer's field guide
What every line on a Certificate of Analysis means, which fields actually matter for your application, and how to spot a doctored document.
Published May 2, 2026 · 7 min read · By PeptideXpo Regulatory Team
A Certificate of Analysis is the single most important document in peptide procurement, and the most common place where buyer attention falls short. This guide walks through every field on a standard COA and explains which ones determine whether a lot is fit for your application.
Header section
A real COA opens with:
- Product name + CAS (or "blend — see attached" for multi-component formulations)
- Batch / Lot number (alphanumeric, traceable to a single production run)
- Manufacturing date + retest date
- Storage condition
- Supplier name, address, and signatory
If any of these are blank or generic, the document is not a COA — it's marketing material with a logo on it.
Identity section
- HPLC purity: target ≥99% for research-grade, ≥99.5% for compounding pharmacy use
- Mass spectrometry: actual MW within tolerance of theoretical (typically ±0.5 Da)
- Sequence verification: required for any peptide >5 amino acids in your QA process
Composition section
- Peptide content (%): typically 75–90% by mass after counter-ion + water adjustment
- Counter-ion: usually acetate or TFA; matters for downstream formulation
- Water content: ≤8% for lyophilized vials (higher suggests aging or hygroscopy)
- Residual solvents: trace acetonitrile, methanol, etc. — check against your local pharmacopoeia limits
Microbiology section
For injectable-route material:
- Endotoxin (LAL): <0.25 EU/mg is a common compounding-pharmacy threshold
- Microbial limits: total aerobic, total yeast/mold, absence of specified pathogens
Red flags
- "Conforms" without a numeric result
- Identical COA values across multiple lots (suggests templating, not testing)
- COA dated before manufacturing date
- No third-party lab signature where the supplier claims independent verification
What we ship
Every PeptideXpo shipment includes a batch-specific COA covering all of the above, plus the HPLC chromatogram and mass-spec spectrum on request. If anything on our COA doesn't match what you measure in-house, our QA team will work through the discrepancy with you within one business day.