Guide

How to read a peptide certificate of analysis (COA)

Reviewed 22 October 2026 · How we research

A certificate of analysis is the only evidence you have that a vial contains what the label says. Here is how to tell a meaningful one from a decorative one.

What HPLC measures

High-performance liquid chromatography (HPLC) separates the contents of a sample. The result is a chromatogram — a graph of peaks over time. Purity is the area of the main peak as a percentage of all peaks. “99% purity” means 99% of what the detector saw was the main compound.

HPLC purity does not confirm identity — a pure sample of the wrong peptide would still show one clean peak.

What mass spectrometry adds

Mass spectrometry (MS) measures molecular weight. If the observed mass matches the expected mass (for example ≈ 1,419 Da for BPC-157), identity is confirmed. A credible COA has both HPLC purity and MS identity.

COA checklist

• Batch/lot number that matches the vial label.
• Test date — recent, and after the batch was made.
• Lab name that you can look up; ideally independent of the seller.
• Chromatogram image, not just a number.
• Mass spec result with expected vs observed mass.
• Quantity/content — some tests also measure actual mg per vial, which purity alone does not.

Red flags

• Identical COA reused across many batches or products.
• No chromatogram, or one with no axis labels.
• Lab name that does not exist or cannot be contacted.
• Purity stated as exactly 99.9% on every product.
• No batch number on the vial.