HPLC purity

High-performance liquid chromatography (HPLC) is the industry standard for measuring peptide purity. When a peptide has a stated HPLC purity percentage, that figure should come from a calibrated HPLC system, typically using a reverse-phase C18 column with a UV detector at 214 nm or 220 nm. Each peak in the chromatogram represents a distinct molecular species; the area under the target peak, expressed as a percentage of the total peak area, is the purity figure. For research peptides, very high purity values should still be reviewed alongside any extra batch tests that were actually run, without treating purity as proof of molecular identity. The choice of UV detection wavelength matters: 214 nm captures the peptide bond absorption directly and is the most universal setting for peptides; 220 nm is sometimes used to suppress mobile-phase noise but underestimates absorbance for peptides without aromatic residues. Gradient HPLC (varying mobile phase composition over time) separates closely related species - truncated sequences missing one residue, oxidized variants, racemized residues - that would co-elute under isocratic conditions. The full purity report on a Certificate of Analysis should include the column type, mobile phase, gradient program, flow rate, detection wavelength, retention time of the target peak, and a copy of the chromatogram itself. Reviewing all of these is the only way to understand what a stated purity figure means for the relevant batch. Peptra Labs records these parameters in available COA information for eligible batches.