HPLC

High-performance liquid chromatography (HPLC) is the reference analytical technique to separate, identify, and quantify chemical compounds within a complex mixture. For peptides, it is the pivotal quality control tool: it determines batch purity (percentage of main peak relative to total chromatographic integral), identifies impurities (degradation products, truncated sequences, isomers, miscoupled peptides), and confirms structure in combination with mass spectrometry.

The principle relies on a liquid mobile phase (eluent) transporting the sample through a column packed with a microparticulate solid stationary phase (typically 2-5 microns). Compounds interact differently with the stationary phase based on their physicochemical properties and migrate at different speeds, progressively separating into distinct peaks visible on the downstream detector (UV at 214 nm for the peptide bond, 280 nm for aromatic Trp/Tyr/Phe residues). Applied high pressure (100 to 400 bars) allows use of fine particles that dramatically amplify resolution compared to classical chromatography.

For peptides, the dominant mode is reverse-phase chromatography (RP-HPLC), where the stationary phase is hydrophobic (C18 or C8 grafts on silica) and the mobile phase is an aqueous/organic mixture (water + acetonitrile or methanol, supplemented with 0.1% trifluoroacetic acid or formic acid). Elution follows a linear gradient of increasing organic, where hydrophilic peptides elute first and hydrophobic ones later. A typical RP-HPLC column (250 mm x 4.6 mm, 5 microns) achieves theoretical resolution of 10,000 to 20,000 plates, i.e., the capacity to separate hundreds of distinct peaks.

HPLC purity is the central criterion of research peptide certificates of analysis (COA). Industry standards are: >95% for routine use, >98% for rigorous in vivo applications, >99% for clinical trials. Purity calculation integrates the main peak area and divides it by total area of all peaks detected above noise threshold. At Lab Peptides France, our published Janoshik analyses measure 99.4 to 99.9% HPLC purity, verifiable online with their key.

Beyond purity, HPLC offers two other critical dimensions. First, quantification: once calibrated with external standards, HPLC precisely measures absolute peptide mass in a sample, a parameter essential to calibrate experimental concentrations. Second, coupling to mass spectrometry (LC-MS and LC-MS/MS) enables identification of each peak by molecular mass, and even sequencing impurities to understand degradation pathways. This HPLC-MS combination is today the gold standard for characterizing a research peptide.