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

• Published in: Analytical chemistry (Washington) 2011-05, Vol.83 (12), p.4962-4969
• Main Authors: Melvin Blaze, M.T., Takahashi, Lynelle K., Zhou, Jia, Ahmed, Musahid, Gasper, Gerald L., Pleticha, F. Douglas, Hanley, Luke
• Format: Article
• Language: English
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac200693h

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 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 ~8.3±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.