COA

A Certificate of Analysis (COA) is a vendor-issued document — ideally from an independent third-party lab — reporting the identity and purity of a specific peptide batch. The two most relevant numbers on a COA are mass-spec confirmation of identity (does the molecule match the expected mass?) and HPLC purity (typically reported as area-percent at a specified wavelength).

Reputable peptide vendors publish per-batch COAs accessible by lot number. Generic COAs that do not reference a specific lot are essentially marketing material and should not be treated as quality evidence.

The most-cited independent labs for peptide COAs are Janoshik Analytical and a small handful of others. Cross-batch consistency from a vendor — multiple batches at >95% HPLC purity over time — is a stronger quality signal than a single high-purity COA.