Mass spectrometry
In short A method that measures the mass of molecules to confirm the identity of a peptide.
A mass spectrometer turns molecules into charged particles and measures their mass-to-charge ratio. For a peptide, the measured mass is compared with the theoretical mass calculated from its sequence. A match within the instrument's tolerance confirms that the substance is the one named.
Mass spectrometry and HPLC answer different questions. Mass spectrometry asks "is this the right molecule?"; HPLC asks "how much of the sample is that molecule?". A complete identity and purity check therefore often uses both, sometimes coupled in one instrument (LC-MS).
Peptides often appear in a spectrum as several peaks carrying different numbers of charges. Software combines them to give the molecular mass. Small differences from the theoretical value can indicate a modification, such as oxidation of a methionine residue, which is useful to know for sensitive sequences.
Where a certificate in our library reports identity confirmation, the method is named on the PDF.