What Is HPLC? (Plain-English Guide for Peptide Buyers)
HPLC is the analytical method behind every legitimate peptide purity claim. Here is what the acronym means, how the test works, and how to read the chromatogram on a supplier's COA.
High Performance Liquid Chromatography is the analytical method behind almost every legitimate peptide purity number you will see on a supplier's Certificate of Analysis. The chromatogram printed on a COA is the source data; the purity percentage is just a calculation derived from it.
This guide explains what HPLC is, how the test works in plain English, and how to read the resulting chromatogram without a chemistry background.
For laboratory research use only.
What HPLC is and how it works
HPLC stands for High Performance Liquid Chromatography. It is a separation technique that takes a liquid sample, pushes it through a packed column under high pressure, and sorts the components by how strongly each one interacts with the column material.
The peptide sample is dissolved in a solvent and injected into the instrument. A pump drives the sample through a long, narrow stainless steel tube — the column — which is packed with tiny silica particles. Different molecules stick to the silica with different affinities. The ones that stick less come out first. The ones that stick more come out later. The time each component takes to travel through the column is called its retention time.
At the far end of the column, a UV detector watches the liquid stream and records every time a molecule passes through. Peptides absorb ultraviolet light strongly at 220nm, the wavelength of the peptide bond, so a detector tuned to 220nm sees a clean signal whenever peptide material elutes.
The output is a graph called a chromatogram. Time runs along the X-axis. Detector signal runs up the Y-axis. Every compound in the sample shows up as a peak at its retention time. A pure peptide produces one tall, narrow peak at the expected retention time; a degraded or under-purified sample produces additional peaks alongside it.
The purity percentage on a COA is calculated by integrating the area under each peak and reporting the target peak as a fraction of the total peak area. A 99% purity result means the target peak accounts for 99% of the total signal — the other 1% is everything else in the vial.
How to read a chromatogram
Three things matter when you look at an HPLC chromatogram on a peptide COA:
The retention time of the main peak. Every peptide has a published retention time on a given column and method. BPC-157, Semaglutide, and TB-500 each elute at characteristic times. If the main peak on the chromatogram is not at the expected retention time, the sample is not what the label says it is.
The shape of the main peak. A clean, symmetric, narrow peak indicates a well-resolved compound. A broad, lopsided, or split peak suggests either degradation or co-eluting impurities — meaning two compounds are coming out of the column at almost the same time and the method cannot separate them.
The presence and size of side peaks. Small additional peaks are normal; no synthesis is perfectly clean. They become a problem when they are large. A side peak that is 5% the height of the main peak is real impurity. Two or three side peaks of comparable size to the main peak indicate a mixture, not a purified peptide.
For a full walkthrough of what else should appear on a real COA, see our guide to reading a peptide Certificate of Analysis.
Why HPLC matters when choosing a supplier
A supplier that publishes a full HPLC chromatogram with every batch is doing two things at once. They are showing the underlying data — not just a percentage that could be fabricated — and they are inviting independent verification, since the same sample can be sent to a third-party lab and the resulting chromatogram should match.
A supplier that publishes only a purity number, with no chromatogram, no retention time, and no method, is publishing a marketing claim. The number could be correct. There is no way to know.
This is why, in our 2026 Annual Purity Report, the strongest filter for evaluating suppliers was not the headline purity number — it was whether the chromatogram was present at all, and whether it matched the batch number on the vial. Most of the suppliers we surveyed failed that test.
For research use only. Not for human consumption.
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