Understanding Purity Testing

High-performance liquid chromatography separates the contents of a sample into peaks as they elute from a column. The area of the main peak versus everything else gives you the purity percentage.

Mass spectrometry weighs molecules. By comparing the measured molecular weight against the theoretical weight for your peptide sequence, you confirm the molecule on the chromatogram is the molecule on the label.

HPLC alone tells you something is pure — not what it is. Mass spec alone tells you the right molecule is present — not whether contaminants are too. You need both for a defensible result.