SINGLE-PHOTON AND MULTIPHOTON IONIZATION OF INFRARED LASER-DESORBED BIOMOLECULES

Results from investigations of the 10.5 eV photoionization of infrared laser-desorbed, jet-entrained peptides are presented. The instrumental set-up for vacuum ultraviolet generation and the coupling to a reflectron-time-of-flight mass spectrometer is described. Single-photon ionization makes possible the investigation of molecules without any chromophoric group. Examples of the application of this ionization method to di- and tripeptides containing glycine, alanine, leucine and proline are shown. A comparison between single- and multi-photon ionization of tryptophan and tryptophan-containing peptides up to four amino acids is made and discussed in terms of soft ionization and generation of fragment ions.