High-Performance Liquid Chromatography (HPLC) is the standard analytical method for assessing peptide purity. It separates the components of a sample so the target peptide can be quantified against any impurities, with the result expressed as a purity percentage.
A result of "≥99% by HPLC" indicates that the contents of the vial are almost entirely the named peptide, with minimal by-products from synthesis. Mass spectrometry is a complementary technique that confirms the molecular weight and therefore the identity of the compound.
Independent, third-party testing matters because it removes reliance on a supplier's own claims. A Certificate of Analysis (CoA) documents the batch result and is the primary evidence a researcher should expect before using any material.
Every Onyx Peptides batch is independently HPLC-tested, with the CoA available on request. Purity is not a marketing figure, it is the difference between a usable research reference material and an unknown.
This article is provided for educational and research-reference purposes only. It is not medical advice. All products are supplied strictly for in-vitro laboratory research use, not for human or veterinary consumption.
Reference: Research Peptide Purity & Testing — a full guide.