Peptide Fundamentals · 7 min read · March 18, 2026
Understanding Research Peptide Purity
What 99% HPLC really means — and why the test method matters more than the number.
Dr. Mira Halden
Chief Scientific Officer
What purity measures
When a supplier prints 99% on a label, they are almost always referring to the result of a reverse-phase high-performance liquid chromatography (RP-HPLC) assay. The column separates molecules by polarity, and a UV detector records a chromatogram: peaks that represent everything passing through the detector at a given wavelength.
Purity, in that context, is the area of the target peptide peak divided by the total area of every peak on the chromatogram. If your target peptide is 99% of the total integrated area, the remaining 1% is process-related impurities: truncated sequences, deletion peptides, oxidized variants, or co-eluting fragments.
What purity does not measure
HPLC purity is not the same as total content. A vial can be 99% pure by HPLC and still contain residual water, salts, or counter-ions that dilute the total peptide mass. That is why a rigorous Certificate of Analysis reports purity, mass-spec confirmation, and peptide content separately.
A 99% peak can also be blind to structural isomers. If an impurity co-elutes with the target, it will not appear on the chromatogram at all. This is why the detection wavelength, the gradient, and the column chemistry matter as much as the headline number.
How to read a purity report critically
Look for the detection wavelength (220nm is standard for peptide bonds). Check for a second orthogonal method — LC-MS is the gold standard for confirming the molecular weight of the main peak. And look for the full chromatogram, not just the summary figure.
A lab that publishes the raw trace is communicating confidence. A lab that only publishes a number is asking you to trust them. Verdaine publishes both.
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