What 99% Purity Actually Means: HPLC, Mass Spec, and Reading a CoA

A Certificate of Analysis tells you what's in the vial. but only if you know how to read it. The headline 'purity %' on most CoAs is the area under the main HPLC peak as a percentage of total integrated peak area. That number changes based on detector wavelength, column chemistry, and integration cutoffs.

Mass spectrometry tells you whether the molecule is the right molecule. A peptide can be 99.5% pure by HPLC and still be the wrong sequence. an isomer, an oxidation product, or a TFA adduct. Both tests together are the minimum standard for serious research work.

Things to look for on a CoA: identity confirmation by ESI-MS or MALDI-TOF with observed mass within 1 Da of theoretical; HPLC trace with the main peak well-resolved from impurities; residual solvent and water content disclosed; lot number and manufacture date present; analyst signature.

Things that are red flags: missing mass-spec data, single-peak chromatograms with no impurity profile, no lot traceability, or 'purity ≥98%' with no actual chromatogram attached. Orvion publishes the full HPLC + MS pair for every lot. ask for it before ordering.