7.87 eV laser desorption postionization mass spectrometry of adsorbed and covalently bound bisphenol A diglycidyl methacrylate

Laser desorption postionization for imaging MS of biological material

Vacuum ultraviolet single photon ionization (VUV SPI) is a soft ionization technique that has the potential to address many of the limitations of matrix-assisted laser desorption/ionization (MALDI) for imaging MS. Laser desorption postionization (LDPI) uses VUV SPI for postionization and is experimentally analogous to a MALDI instrument with the addition of a pulsed VUV light source. This review discusses progress in LDPI-MS over the last decade, with an emphasis on imaging MS of bacterial biofilms, analytes whose high salt environment make them particularly resistant to imaging by MALDI-MS. This review first considers fundamental aspects of VUV SPI including ionization mechanisms, cross sections, quantum yields of ionization, dissociation and potential mass limits. The most common sources of pulsed VUV radiation are then described along with a newly constructed LDPI-MS instrument with imaging capabilities. Next, the detection and imaging of small molecules within intact biofilms is demonstrated by LDPI-MS using 7.87 eV (157.6 nm) VUV photons from a molecular fluorine excimer laser, followed by the use of aromatic tags for detection of selected species within the biofilm. The final section considers the future prospects for imaging intact biological samples by LDPI-MS.

Light and molecular ions: the emergence of vacuum UV single-photon ionization in MS

Thanks to recent technological advances and single-photon ionization's (SPI's) ability to detect all organics, the technique could become the long-sought universal soft ionization method. (To listen to a podcast about this feature, please go to the Analytical Chemistry Web site at pubs.acs.org/journal/ancham.).

Laser desorption 7.87 eV postionization mass spectrometry of antibiotics in Staphylococcus epidermidis bacterial biofilms

This paper describes the development of laser desorption 7.87 eV vacuum UV (VUV) postionization MS to detect antibiotics within intact bacterial colony biofilms. As >99% of the molecules ejected by laser desorption are neutrals, VUV photoionization of these neutrals can provide significantly increased signal as compared to the detection of directly emitted ions. Postionization with VUV radiation from the molecular fluorine laser single photon ionizes laser desorbed neutrals with ionization potentials below the 7.87 eV photon energy. Antibiotics with structures indicative of sub-7.87 eV ionization potentials were examined for their ability to be detected by 7.87 eV laser desorption postionization MS. Tetracycline, sulfadiazine, and novobiocin were successfully detected neat as dried films physisorbed on porous silicon oxide substrates. Tetracycline and sulfadiazine were then detected within intact Staphylococcus epidermidis colony biofilms, the former with LOD in the micromolar concentration range.

Infrared laser desorption/vacuum ultraviolet photoionization mass spectrometry of petroleum saturates: a new experimental approach for the analysis of heavy oils

A novel method combining infrared (IR) laser desorption with tunable synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (LD/VUV PIMS) is applied to characterize a number of petroleum saturates samples from Lungu atmospheric residue (LGAR) under different treatment procedures. The mass spectra of these saturates are well resolved with even masses as the dominant ions and are clearly sample-dependent. In order to assess the ability of IR LD/VUV PIMS to determine the average molecular weight of heavy oils, the dependence of the measured molecular weight distributions on the VUV ionization photon energies is also discussed.