HPLC for Peptide Purity Verification — A Practical Overview

High-performance liquid chromatography is the workhorse purity assay for synthetic peptides. The method separates compounds in a mixture based on how strongly each interacts with a stationary phase under a gradient of mobile-phase composition.

Why reverse-phase

Reverse-phase HPLC uses a non-polar stationary phase (typically C18) and a polar mobile phase (water-acetonitrile gradients with TFA modifier). Peptides distribute between phases according to their hydrophobicity, so a peptide elutes when the mobile phase reaches a composition that overcomes its retention on the column.

Reading a chromatogram

• The x-axis is retention time — when in the gradient a species came off the column.
• The y-axis is detector response, typically UV absorbance at 220 nm for peptide bonds.
• A sharp, symmetric main peak with minimal area in adjacent regions indicates high purity.
• Broad peaks, fronting, or tailing suggest column overload, sample degradation, or co-elution.

Purity calculation

Purity by HPLC is the ratio of the main peak area to the total integrated area, expressed as a percentage. The chosen integration window matters: a too-narrow window inflates the number, a too-wide one captures noise. Reputable labs publish their integration method alongside the percentage.