Superimposition and Analysis of ESI Tandem Mass Spectra

Methionine enkephalin and four synthetic peptides (a heptapeptide and its modified form, a decapeptide and an icosapeptide) were fragmented using ESI tandem mass spectrometry with certain varying instrumental parameters, such as amplitude of excitation, to produce a series of MS/MS spectra. Using the Bruker DataAnalysis software, some complementary MS/MS spectra were chosen to form a superimposed MS/MS spectrum with consecutive triplets (as well as a few doublets) consisting of product ions AnBnCn or X n Y n Z n. The amino acid sequences of the peptides were easily and accurately determined from the superimposed MS/MS spectrum, suggesting that the method is easy and suitable for peptide sequencing by tandem mass spectrometry.