Mass Spectrometry for Peptide Identity

Mass spectrometry ionises a sample and measures the mass-to-charge ratio of the resulting ions. For peptides, the result is a precise molecular weight that should match the theoretical weight calculated from the amino acid sequence.

Theoretical and measured masses should agree within instrument tolerance — typically a few daltons for low-resolution instruments, fractions of a dalton for high-resolution.

HPLC tells you 'a single dominant compound is present'. Mass spec tells you 'and that compound is the one on the label'. Without mass spec, identity confirmation is essentially trust.

This matters because peptide synthesis can produce closely related sequences with similar HPLC behaviour but different molecular weights — for instance, a peptide missing one amino acid, or with a wrong residue. Mass spec catches these.

Is mass spec data on the COA? If not, why not? What was the measured molecular weight, and how does it compare with theoretical? What instrument was used (low-res vs high-res affects the tolerance)?