How to read a certificate of analysis

A certificate of analysis is only useful if it is tied to the lot in your hand. The first thing to check is not the purity figure but the lot number — if it does not match the vial label, the document tells you nothing about your material.

HPLC purity is reported as a percentage of total peak area. A figure above 98% is a reasonable expectation for a research peptide. Look at the chromatogram itself where it is provided: one dominant peak with a clean baseline is a better signal than a number typed on a page.

Mass spectrometry answers a different question — identity rather than cleanliness. The observed mass should sit within a fraction of a dalton of the theoretical mass for the sequence. A purity result without an identity result is half a report.

Water content matters more than most buyers expect. Residual moisture in a lyophilised cake accelerates degradation, so a Karl Fischer or loss-on-drying figure is worth having.

Finally, check who signed it. Independent third-party testing carries weight that in-house testing does not, and a dated signature with a laboratory name is the difference between a report and a graphic.