A certificate of analysis is a claim sheet, not a guarantee. Here is what HPLC area%, mass spec identity, endotoxin and sterility lines each do and do not establish — and which questions to ask when a line is missing.

Area percent is the most quoted and least understood number on a peptide certificate. A short methods note on detection thresholds, co-elution, and why two labs can honestly report different purity for the same vial.

A pentadecapeptide derived from a gastric juice protein, with a large rodent literature and a thin clinical one. A neutral map of where the evidence stands, what models dominate it, and where the gaps are.

Mass, volume and concentration are one equation. A worked reference for converting a vial's milligrams into a working solution of known micrograms-per-microliter, with the unit traps that cause most bench errors.

Lyophilization buys stability by removing water; every handling decision after that is a decision about letting water back in. A practical note on storage states, desiccation, and freeze-thaw discipline.

The cheapest signal of a serious supplier is not price or purity number — it is whether a certificate can be tied to the exact unit you received. How to test traceability before you buy.