How to read a certificate of analysis (COA) — the concepts

A vendor-neutral primer on what testing numbers actually mean (concepts only — this isn't sourcing advice):

• HPLC purity (%) estimates how much of a sample is the target peptide vs. related impurities. Higher is better, but a number is only as good as the method and the sample tested.
• Mass spec (MS) identity checks that the molecular weight matches the intended peptide — i.e., is it actually the thing it claims to be?
• A COA describes the tested sample, not necessarily any other lot. Lot-to-lot variation is real.

What a COA can't tell you: sterility, endotoxin status (unless explicitly tested), or anything about safety in a person.

Treat purity data as one input for understanding the literature — not as a green light. Educational only.