What is peptide purity?
Peptide purity is the share of the detected material in a sample that is the target peptide, usually reported as the main peak's percentage of total peak area in an HPLC chromatogram.
How purity is calculated
The HPLC software measures the area under every peak in the chromatogram. Purity is the main peak's area divided by the total area of all integrated peaks. A result of 99.90% means 0.10% of the detected peak area belongs to other components.
Purity is relative, not absolute
Purity describes the detected material only. A lyophilized peptide powder also contains water, residual salts and counterions such as acetate, which produce little or no UV signal. Purity therefore is not the same as peptide content (how much of the powder's weight is peptide) or net content (how many milligrams of peptide are in the vial).
Typical impurities in synthetic peptides
Deletion sequences missing one residue, truncated chains, sequences with a protecting group left on, mirror-image forms of single residues, and oxidized or deamidated forms that arise during storage.
Melanotan I purity
The release specification is ≥95% by HPLC-UV. Current lots report 97.55%. Each figure applies only to the lot tested.