Why a purity percentage is only half of a certificate of analysis.
Every peptide vendor claims high purity. Here is what the number means, and what it does not tell you.
High-performance liquid chromatography separates the components of a sample and measures each as a peak. Purity is the target peak's share of the total peak area, typically read at 220 nm. A result of 99% means 99% of the detected peak area is the main peak.
HPLC does not by itself prove the main peak is the compound on the label. It also does not measure water, salts, or counter-ions, so "purity" is not the same as net peptide content.
Mass spectrometry confirms identity by measuring molecular weight. A real COA pairs HPLC purity with an MS result that matches the expected mass for that compound.
Check that the report names the specific batch or lot number, shows the actual chromatogram (not just a number), lists the testing lab and date, and includes an identity result. The full 7-point checklist is here →
Written for a research audience. Midas products are for laboratory research use only.