Brominated Tyrosine and Polyelectrolyte Multilayer Analysis by Laser Desorption Vacuum Ultraviolet Postionization and Secondary Ion Mass Spectrometry

摘要

The small molecular analyte 3,5-dibromotyrosine (Br_(2)Y) and chitosan-alginate polyelectrolyte multilayers (PEM) with and without adsorbed Br_(2)Y were analyzed by laser desorption postionization-mass spectrometry (LDPI-MS). LDPI-MS using a 7.87 eV laser and tunable 8-12.5 eV synchrotron vacuum ultraviolet (VUV) radiation found that desorption of clusters from Br_(2)Y films allowed detection by <=8 eV single photon ionization. Thermal desorption and electronic structure calculations determined the ionization energy of Br_(2)Y to be approx8.3 +- 0.1 eV and further indicated that the lower ionization energies of clusters permitted their detection at <=8 eV photon energies. However, single photon ionization could only detect Br_(2)Y adsorbed within PEMs when using either higher photon energies or matrix addition to the sample. All samples were also analyzed by 25 keV Bi_(3)~(+) secondary ion mass spectrometry (SIMS), with the negative ion spectra showing strong parent ion signal which complemented that observed by LDPI-MS. However, the negative ion SIMS appeared strongly dependent on the high electron affinity of this specific analyte and the analyte's condensed phase environment.