A Certificate of Analysis (COA) is the lab report documenting what's actually in a specific batch of peptide, and how it was verified. Two analytical methods do almost all of the work: HPLC (High-Performance Liquid Chromatography) for purity, and mass spectrometry for identity confirmation.
HPLC separates every compound in the sample by how it interacts with a chromatography column, producing a chromatogram — a graph of peaks. Purity is calculated as the main peptide peak's share of the total peak area: a 99% purity result means 99% of all detected material is the intended peptide, and roughly 1% is something else (a synthesis byproduct, a truncated sequence, residual solvent). Mass spectrometry independently confirms identity by comparing the observed molecular weight against the theoretical weight calculated from the peptide's amino acid sequence — a match confirms the right amino acids are present in the right order.
A proper COA should list the peptide's name and sequence, batch/lot number, purity percentage, the specific test methods used, and the issuing laboratory's credentials. ≥98% purity is generally considered the research-grade standard, appropriate for the reproducibility that laboratory and preclinical work requires.
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