How to Read a Research Peptide COA
A peptide COA can look intimidating: mass spec traces, HPLC percentages, endotoxin numbers in EU/mg. Once you know what each section is for, reading one takes about a minute. This guide walks through a typical PX1 COA end to end.
Header block: what lot are you looking at?
Lot number, manufacture date, expiry, quantity per vial, and storage condition. Confirm the lot number matches the vial in your hand.
Purity row
Reported as a percentage — the fraction of total HPLC peak area attributable to the target peptide. ≥99% is the PX1 standard for research-grade material.
Identity row
Observed molecular mass vs theoretical mass. Within ±1 Da is expected on LC-MS for most peptides.
Net peptide content
Actual peptide mass per vial after subtracting counter-ion and moisture. Use this — not gross vial fill — for molar calculations.
Endotoxin
Reported in endotoxin units per milligram (EU/mg). For most research applications, <10 EU/mg is acceptable; for cell culture and in-vivo work, lower thresholds apply.
Signature line
A signed COA from a named QA release ties the document to a person — not just an anonymous PDF.
Frequently Asked Questions
What does 99% HPLC purity mean?
That 99% of the total UV peak area in the HPLC chromatogram is the target peptide. The remaining 1% is process impurities, most of which are structurally related.
What does EU/mg mean on a peptide COA?
Endotoxin units per milligram of peptide, measured by LAL. It quantifies bacterial endotoxin contamination — lower is better.
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