How to Evaluate Peptide Purity
Methods for assessing purity claims and understanding what HPLC and mass spec results actually tell you.
Last updated: 17 April 2026
What purity means
Purity is the percentage of the desired peptide by mass in the sample. A 95% pure peptide contains 95% target compound and 5% other material. Impurities may include related peptides, degradation products, salts, or residual solvents.
Higher purity usually indicates better manufacturing and purification, but cost increases substantially at very high purities.
Understanding HPLC purity
High-performance liquid chromatography separates compounds. A report showing a single large peak and no significant others suggests high purity. Check the chromatogram itself, not just the summary percentage.
Be alert to: integration windows that exclude real impurity peaks, missing axis labels, or reports that quote a number without the actual trace.
Mass spectrometry confirmation
Mass spectrometry determines the molecular weight. If the measured mass matches the theoretical mass of the peptide within instrument tolerance (usually ±0.05%), this confirms identity.
Mass spec does not directly measure purity — but it confirms you have the right compound, not a different one.
Purity red flags
Generic claims like '99% pure' without method details. Same COA across different batches. No supporting chromatograms. Purity above 99% claimed without third-party confirmation. Suppliers unable to explain how purity was measured.