What do purity and net peptide content mean on a COA?

Question

pepmg · Accepted Answer

Purity is the fraction of the peptide present that is the right molecule, measured by HPLC and reported as a percentage; research-grade is typically at or above 98 percent. Net peptide content is a different number: how much of the vial's labeled mass is peptide at all, since the rest is counter-ion salt and residual water left from freeze-drying.

The gap between them is money. A batch can be highly pure and still run well under full net content, so a labeled vial holds less actual peptide than the sticker implies — which quietly makes the real $/mg higher. Net content is rarely published because it needs extra analysis, so when a COA reports it, that is a real transparency signal and the most honest basis for $/mg there is.