LC-MS (liquid chromatography–mass spectrometry) couples an HPLC separation with a mass spectrometer, so that each chromatographic peak is analysed to yield an accurate mass of the eluting species. For peptides, the most common ionisation method is electrospray (ESI), which produces multiply charged ions from which the intact monoisotopic or average mass can be deconvolved.
For research peptides, LC-MS is used to confirm identity by matching the observed mass to the theoretical mass calculated from the primary sequence and any declared modifications. It can also detect major synthesis- and stability-related impurities such as truncated sequences, deamidation or oxidation products.
LC-MS identity confirmation complements HPLC purity on the Certificate of Analysis and is the primary evidence that the supplied compound is the compound the label claims.