Understanding the analytical methods used to test peptide purity helps buyers evaluate COA documentation and understand what each test actually confirms — and what it doesn't.
High-Performance Liquid Chromatography (HPLC)
HPLC separates compounds based on their interaction with a stationary phase and mobile phase. For peptides, reverse-phase HPLC (RP-HPLC) is standard — it separates based on hydrophobicity. The result is a chromatogram showing peaks for each compound in the sample. Purity is calculated as the area of the target peak divided by total peak area. HPLC measures purity but cannot confirm identity — a contaminant with similar hydrophobicity to the target peptide would not be detected.
Mass Spectrometry (MS)
Mass spectrometry measures the mass-to-charge ratio of ionized molecules, providing the molecular weight of each compound in the sample. For peptide verification, the measured molecular weight must match the theoretical molecular weight of the correct sequence. This is the only way to confirm that the correct peptide was synthesized — HPLC purity alone cannot distinguish between a correct peptide and a different peptide with similar chromatographic properties.
Why Both Are Required
A complete peptide COA requires both HPLC purity (≥98%) and MS molecular weight confirmation. HPLC without MS confirms purity but not identity. MS without HPLC confirms identity but not purity. Both tests together confirm that the correct compound is present at the required purity level. Any COA missing either test is incomplete.