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

Abstract

The small molecular analyte 3,5-dibromotyrosine (Br2Y) and chitosan-alginate polyelectrolyte multilayers (PEM) with and without adsorbed Br2Y 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 Br2Y films allowed detection by ≤8 eV single photon ionization. Thermal desorption and electronic structure calculations determined the ionization energy of Br2Y 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 Br2Y adsorbed within PEMs when using either higher photon energies or matrix addition to the sample. All samples were also analyzed by 25 keV Bi3+ 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.

Differentiation of microbial species and strains in coculture biofilms by multivariate analysis of laser desorption postionization mass spectra

“…Overall, 10.5 eV photon energy displayed an optimal balance between sensitivity and fragmentation, in agreement with prior experiments. 26, 27, 35 Similar conclusions were reached from 7.87 – 10.5 eV synchrotron LDPI-MS of E. coli (tomato strain) monoculture blots (full mass spectra shown in Supplementary Information). The mass spectral peaks observed for E. coli and yeast monocultures were tabulated with the VUV photon energies at which they were first observed by synchrotron LDPI-MS (see Supplementary Information).…”

“…Prior control experiments with the 10.5 eV laser LDPI-MS established the presence of single photon ionization and ruled out both direct ions from laser desorption and photoelectron ionization effects due to the residual 355 nm beam used to generate VUV radiation. 25 Photoelectron ionization was previously ruled out in the synchrotron LDPI-MS. 27 The similarity of the spectra of 7.87 eV synchrotron and laser LDPI-MS ruled out photoelectron ionization in the latter case.…”

“…Prior synchrotron LDPI-MS studies 26, 27 led to the recent development of a refined laboratory VUV photoionization source that operates at 10.5 eV 25 to complement the 7.87 eV fluorine excimer laser source. 22 These two laboratory laser VUV sources were used to collect 7.87 and 10.5 eV laser LDPI-MS data from yeast and E. coli monocultures.…”

“…Prior LDPI-MS work showed that the higher VUV photon energies in the range of 7.8 – 12.5 eV improved sensitivity and produce intense molecular ion signal, but leads to formation of fragment ions and background gas ions. 26, 27 Because the 10.5 eV photon energy appeared to provide the optimal balance between improved sensitivity and minimal fragmentation, a more robust laboratory source of 10.5 eV radiation was recently developed. 25 …”

Quantification of Antibiotic in Biofilm-Inhibiting Multilayers by 7.87 eV Laser Desorption Postionization MS Imaging

“…Several peaks at m/z 270.1 and below m/z 150 appeared from desorption laser-induced pyrolysis of the multilayer. 9 The bottom and top traces show mass spectra before and after UV sterilization, respectively, again indicating no significant differences in the fragmentation pattern of MPA-ampicillin. It is concluded that photolysis or other modification of the antibiotic or multilayer did not result from UV sterilization.…”