Development of tandem time-of-flight instrumentation for the examination of prompt photodissociation of peptides using 193-nm radiation

The design and incorporation of a decelerating/accelerating cell into a reflectron time-of-flight mass spectrometer is described for the examination of promptly-formed photodissociation products of peptide ions. The analytical utility of prompt 193-nm photodissociation was investigated for model peptides that resemble tryptic digest products, as well as for two sets of homologous peptides. The first of these sets include bradykinin, several bradykinin fragments, and two bradykinin mutants with substituted amino acids. Fragment ion spectra of [M + H]+, [M + Na]+, and [M + Cu]+ were collected for each of these peptides. The second set of homologous peptides has the sequence XVGVAZG, where variable amino acid X was either arginine, histidine, or lysine, and amino acid Z was either proline, serine, or glycine. Photofragment ion spectra obtained using the new mass spectrometer are compared to results of high energy collision induced dissociation (CID) acquired on a high performance commercial instrument. The advantages and disadvantages of prompt photodissociation relative to CID are discussed, as well as the advantages of photodissociation using the modified instrument geometry versus that of the post-source decay focusing method.