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Download fileTransmission Geometry Laser Desorption Atmospheric Pressure Photochemical Ionization Mass Spectrometry for Analysis of Complex Organic Mixtures
journal contribution
posted on 2014-11-18, 00:00 authored by Leonard Nyadong, Mmilili M. Mapolelo, Christopher
L. Hendrickson, Ryan P. Rodgers, Alan G. MarshallWe present laser desorption atmospheric
pressure photochemical
ionization mass spectrometry (LD/APPCI MS) for rapid throughput analysis
of complex organic mixtures, without the need for matrix, electric
discharge, secondary electrospray, or solvents/vaporizers. Analytes
dried on a microscope slide are vaporized in transmission geometry
by a laser beam aligned with the atmospheric pressure inlet of the
mass spectrometer. The laser beam initiates a cascade of reactions
in the region between the glass slide and MS inlet, leading to generation
of reagent ions for chemical ionization of vaporized analyte. Positive
analyte ions are generated predominantly by proton transfer, charge
exchange, and hydride abstraction, whereas negative ions are generated
by electron capture or proton transfer reactions, enabling simultaneous
analysis of saturated, unsaturated, and heteroatom-containing hydrocarbons.
The absence of matrix interference renders LD/APPCI MS particularly
useful for analysis of small molecules (<2000 Da) such as those
present in petroleum crude oil and petroleum deposits. [M + H]+ and M+• dominate the positive-ion mass
spectra for olefins and polyaromatic hydrocarbons, whereas saturated
hydrocarbons are observed mainly as [M – H]+ and/or
M+•. Heteroatom-containing hydrocarbons are observed
predominantly as [M + H]+. [M – H]− and M–• are the dominant negative ions
observed for analytes of lower gas-phase basicity or higher electron
affinity than O2. The source was coupled with a 9.4 T Fourier
transform ion cyclotron resonance mass spectrometer (FTICR MS) to
resolve and identify thousands of peaks from Athabasca bitumen heavy
vacuum gas oil distillates (400–425 and 500–538 °C),
enabling simultaneous characterization of their polar and nonpolar
composition. We also applied LD/APPCI FTICR MS for rapid analysis
of sodium and calcium naphthenate deposits with little to no sample
pretreatment to provide mass spectral fingerprints that enable reliable
compositional characterization.
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transmission Geometry Laser Desorption Atmospheric Pressure Photochemical Ionization Mass Spectrometryion cyclotron resonance mass spectrometerinletpetroleum crude oilPositive analyte ionselectronslidehydrocarbonmatrixlaser beamcalcium naphthenate depositsvaporizedMScharacterizationComplex Organic MixturesWeproton transfer reactionsionization mass spectrometryLD9.4 T FourierFTICRanalysis