HPLC purity explained
High-performance liquid chromatography (HPLC) pushes a dissolved sample through a packed column. Different molecules travel at different speeds and leave the column at different times, where a UV detector records them as peaks.
What the number means
The purity figure is the area of the main peak as a share of all detected peaks. A result of 99% means that 99% of the UV-detected material eluted as the target peptide.
What it doesn't cover
HPLC doesn't identify the main peak on its own, and it doesn't measure water or counter-ions in the powder. That is why identity is confirmed separately by mass spectrometry, and why net peptide content is a different figure.
For research use only. Not for human or veterinary use.