What it measures
Chromatographic purity is the area of the target peak divided by the total area of all peaks, expressed as a percentage. It describes the peptide-related material the method detected.
What it excludes
Anything the method does not detect does not appear. Counter-ions such as acetate or trifluoroacetate are not detected at typical peptide wavelengths. Water is not detected. Salts are not detected.
A vial can therefore be 99% pure by HPLC while a meaningful fraction of the powder is not peptide at all. That is not a contradiction; the two figures answer different questions.
Comparing figures
Two suppliers quoting the same percentage under different methods are not necessarily describing equivalent material. The shallower the gradient, the more closely related impurities are resolved and the more honest the number.
This is why the method line matters as much as the figure, and why a certificate without one is difficult to act on.
Research use only. This page is explanatory and does not recommend any use, quantity or procedure. REVIVE LAB supplies reference materials for laboratory research. These are not medicines and are not for human or veterinary consumption. Anyone considering the use of any compound in humans should do so only under qualified medical supervision.