@article {2432,
	title = {A new broadly tunable (7.4-10.2 eV) laser based VUV light source and its first application to aerosol mass spectrometry},
	journal = {International Journal of Mass Spectrometry},
	volume = {279},
	number = {2-3},
	year = {2009},
	note = {ISI Document Delivery No.: 399TJTimes Cited: 10Cited Reference Count: 78Hanna, S. J. Campuzano-Jost, P. Simpson, E. A. Robb, D. B. Burak, I. Blades, M. W. Hepburn, J. W. Bertram, A. K.},
	month = {Jan},
	pages = {134-146},
	type = {Article},
	abstract = {A laser based vacuum ultraviolet (VUV) light source using resonance enhanced four wave difference mixing in xenon gas was developed for near threshold ionization of organics in atmospheric aerosol particles. The source delivers high intensity pulses of VUV light (in the range of 10(10) to 10(13) photons/pulse depending on wavelength, 5 ns FWHM) with a continuously tunable wavelength from 122 nm (10.2 eV) to 168 nm (7.4 eV). The setup allows for tight (< 1 mm(2)) and precise focusing (mu rad pointing angle adjustability), attributes required for single particle detection. The generated VUV is separated from the pump wavelengths by a custom monochromator which ensures high spectral purity and minimizes absorptive losses. The performance of the source was characterized using organic molecules in the gas phase and optimal working conditions are reported. In the gas phase measurements, photoionization efficiency (PIE) curves were collected for seven different organic species with ionization energies spanning the full wavelength range of the VUV source. The measured appearance energies are very close to the literature values of the ionization energies for all seven species. The effectiveness of the source for single particle studies was demonstrated by analysis of individual caffeine aerosols vaporized by a pulsed CO2 laser in an ion trap mass spectrometer. Mass spectra from single particles down to 300 nm in diameter were collected. Excellent signal to noise characteristics for these small particles give a caffeine detection limit of 8 x 10(5) molecules which is equivalent to a single 75 nm aerosol, or approximately 1.5\% of a 300 nm particle. The appearance energy of caffeine originating from the aerosol was also measured and found to be 7.91 +/- 0.05 eV, in good agreement with literature values. (C) 2008 Elsevier B.V. All rights reserved.},
	keywords = {Aerosol mass spectrometry, analysis, CROSS-SECTIONS, EFFICIENCY, FUEL-RICH FLAMES, GENERATING PARTICLE BEAMS, ION-TRAP, ONLINE, ORGANIC-COMPOUNDS, PARTICULATE MATTER, PHOTOIONIZATION, SINGLE-PHOTON IONIZATION, SURFACE-ANALYSIS, Vacuum ultraviolet light, VACUUM-ULTRAVIOLET PHOTOIONIZATION},
	isbn = {1387-3806},
	url = {<Go to ISI>://000262821900012},
	author = {Hanna, S. J. and Campuzano-Jost, P. and Simpson, E. A. and Robb, D. B. and Burak, I. and Blades, M. W. and Hepburn, J. W. and Bertram, A. K.}
}
@article {2431,
	title = {A study of oleic acid and 2,4-DHB acid aerosols using an IR-VUV-ITMS: insights into the strengths and weaknesses of the technique},
	journal = {Physical Chemistry Chemical Physics},
	volume = {11},
	number = {36},
	year = {2009},
	note = {ISI Document Delivery No.: 491ADTimes Cited: 3Cited Reference Count: 66Hanna, Sarah J. Campuzano-Jost, Pedro Simpson, Emily A. Burak, Itamar Blades, Michael W. Hepburn, John W. Bertram, Allan K.},
	pages = {7963-7975},
	type = {Article},
	abstract = {An investigation of oleic acid and 2,4-dihydroxybenzoic (DHB) acid aerosols was carried out using an aerosol mass spectrometer with pulsed lasers for vaporization and ionization and an ion trap for mass analysis. The extent of ion fragmentation was studied as a function of both vaporization energy and ionization wavelength. Low CO2 laser energies in the vaporization stage and near-threshold single photon ionization resulted in the least fragmented mass spectra. For DHB, only the molecular ion was observed, but for oleic acid fragmentation could not be eliminated. Tandem MS of the main fragment peak from oleic acid was carried out and provided a tool for compound identification. Photoionization efficiency curves were also collected for both DHB and oleic acid and the appearance energies of both parent and fragment ions were measured. Evidence for fragmentation occurring post-ionization is given by the similar appearance energies for both the parent and fragment ions. The results from this study were compared with those from similar experiments undertaken with time-of-flight (TOF) mass analyzers. The degree of fragmentation in the ion trap was considerably higher than that seen with TOF systems, particularly for oleic acid. This was attributed to the long storage interval in the ion trap which allows time for metastable ions to decay. Differences in the degree of fragmentation between the ion trap and TOF studies also provided further evidence for fragmentation occurring post-ionization. For 2,4-dihydroxybenzoic acid, the long delay prior to mass analysis also allowed time for reactions with background gases, in this case water, to occur.},
	keywords = {ATMOSPHERIC PARTICLES, CHEMICAL-ANALYSIS, ENVIRONMENTAL PARTICLES, GENERATING PARTICLE BEAMS, INVERSE FOURIER-TRANSFORM, LASER-DESORPTION/IONIZATION, ORGANIC-COMPOUNDS, QUADRUPOLE ION-TRAP, TRAP MASS-SPECTROMETER, VACUUM-ULTRAVIOLET PHOTOIONIZATION},
	isbn = {1463-9076},
	url = {<Go to ISI>://000269548300022},
	author = {Hanna, S. J. and Campuzano-Jost, P. and Simpson, E. A. and Burak, I. and Blades, M. W. and Hepburn, J. W. and Bertram, A. K.}
}
