How to Read a Certificate of Analysis

Identity

The reported sequence should match the ordered sequence, character for character. Mass-spec data on the COA should fall within tolerance of the calculated monoisotopic mass.

Purity

HPLC purity is reported as area-percent at a stated wavelength, most commonly 214 nm. Anything labeled "purity" without a method and wavelength is not a meaningful number.

Counter-ion and net peptide content

Peptides are typically supplied as acetate or trifluoroacetate salts. The net peptide content — usually 75–90% of the labeled mass — is what actually goes into your molar calculations.

Endotoxin

For any application involving cell culture, endotoxin should be quantified and reported in EU/mg. A missing endotoxin number is a meaningful absence.