Comparison of microprobe two-step laser desorption/laser ionization mass spectrometry and gas chromatography/mass spectrometry studies of polycyclic aromatic hydrocarbons in ancient terrestrial rocks

Microprobe two-step laser desorption/laser ionization mass spectrometry (muL(2)MS) and gas chromatography/ mass spectrometry (GC/MS) were used to analyze polycyclic aromatic hydrocarbons (PAHs) in ancient terrestrial rocks. muL(2)MS provides an in situ analysis of very small samples, records the PAHs with no isomer information, and gives quantitative data on the degree of alkylation of a given PAH series over the complete mass range. GC/MS provides isomer separation and quantitation of PAHs in bitumen but not kerogen, and is limited by sample size. Combination of these techniques allows analysis of very small samples by muL(2)MS with GC/MS confirmation of isomer distributions of the solvent extractable components (bitumen). It was found that the concentration of bitumen within the rock samples affects the PAH alkylation signal for muL(2)MS. At low bitumen concentrations muL(2)MS can produce pyrolysis products from kerogen that is present; however, as bitumen concentrations increase, the PAH distribution from bitumen dominates the signal. (C) 2001 American Society for Mass Spectrometry.