How to Read an HPLC Report: A Methodological Guide for Peptide Research

A certificate of analysis (COA) accompanies every batch from a serious research peptide supplier. But knowing how to read one is another matter. This guide details the elements that make up an HPLC report and how to interpret them.

The chromatogram

The chromatogram is the graphical representation of the separation of the sample's compounds via high-performance liquid chromatography (HPLC). A single sharp, well-defined peak at a stable retention time indicates a homogeneous substance. Multiple secondary peaks or a broad, poorly defined peak suggest the presence of impurities or synthesis byproducts.

Purity (%)

Expressed as a percentage, HPLC purity corresponds to the area of the main peak relative to the total area of all detected peaks. A result ≥99% is considered the standard for serious research use. This figure alone is not sufficient, however: it must be read alongside the chromatogram to verify that no significant peak was omitted from the calculation.

Mass spectrometry confirmation (LC-MS)

Mass spectrometry confirms the molecular identity of the compound by measuring its exact mass, compared to the expected theoretical mass. This step, distinct from the purity measurement, is what guarantees that the compound analyzed is indeed the one claimed — and not an analog or degradation product with a similar retention time.

Complementary tests

• Water content — affects the stability of the lyophilizate and the accuracy of the actual dosage.
• Peptide content (assay) — verifies that the amount of active peptide matches the amount stated on the label, independent of chemical purity.
• Endotoxins — relevant for any use in cellular models or in-vivo research.
• Heavy metals and residual solvents — traces from the synthesis process, to be quantified rather than ignored.

What a good COA should indicate

• A specific batch number, traceable to the tested sample
• The test date and the laboratory or entity that performed the analysis
• The analytical method used (reverse-phase HPLC, LC-MS, etc.)
• Precise numerical results, not just a "conforms" statement

Research use only

This article is provided for methodological purposes regarding the interpretation of certificates of analysis in a laboratory research context. It does not constitute a guarantee of compliance for any particular batch or supplier.