Understanding Peptide Purity Claims

A purity percentage is only interpretable alongside the method used, the batch it describes, the date and the laboratory that produced it. Without those, the number is a marketing claim.

Purity also says nothing about the remaining percentage. Residual solvents, counter-ions, truncated sequences and water content all occupy that space, and they are not equivalent.

Net peptide content

Lyophilised material contains salts and moisture as well as peptide. Net peptide content — how much of the vial's mass is actually the peptide — is a distinct figure from chromatographic purity, and it directly affects concentration calculations.