How to read a certificate of analysis

A certificate of analysis is the single most useful document attached to a research compound. It is also the most misread. Most buyers skim for a number above ninety-nine and stop there, which skips the part of the document that carries the real signal.

Start with identity, not purity. Mass spectrometry confirms the molecular weight of what is in the vial. If the observed mass does not match the theoretical mass of the sequence, the purity figure below it is describing the wrong molecule.

Then read the HPLC chromatogram. Purity is the area of the main peak relative to total peak area. A clean trace shows one dominant peak with a flat baseline. Several small satellite peaks suggest related impurities from synthesis.

Finally, check the lot number against the vial in your hand, and the date the analysis was performed. A COA that does not match your lot is a marketing document, not a test result.