How do I read and verify a peptide COA?

A certificate of analysis (COA) reports what a lab measured for one specific batch. Two tests do the heavy lifting: HPLC (high-performance liquid chromatography) measures purity as the target peak's share of total UV-absorbing peaks, and mass spectrometry (LC-MS) confirms identity by matching the measured molecular mass to the expected peptide. A complete COA names the testing lab, the compound, a batch/lot number, the analysis date, the HPLC purity %, and an MS identity result. The most important step is to verify the report on the lab's own portal rather than trusting the PDF. Independent labs such as Janoshik issue each report a unique key you enter on their verification page, which returns the original measured values; confirm the compound, purity, molecular mass, and date there match your document. Treat a COA as one batch's snapshot — not a guarantee about every vial.