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 (mu L(2)MS) and gas chromatography/ mass spectrometry (GC/MS) were used to anal yze polycyclic aromatic hydrocarbons (PAHs) in ancient terrestrial rocks. m uL(2)MS provides an in situ analysis of very small samples, records the PAH s 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 provid es isomer separation and quantitation of PAHs in bitumen but not kerogen, a nd is limited by sample size. Combination of these techniques allows analys is of very small samples by muL(2)MS with GC/MS confirmation of isomer dist ributions of the solvent extractable components (bitumen). It was found tha t the concentration of bitumen within the rock samples affects the PAH alky lation signal for muL(2)MS. At low bitumen concentrations muL(2)MS can prod uce pyrolysis products from kerogen that is present; however, as bitumen co ncentrations increase, the PAH distribution from bitumen dominates the sign al. (C) 2001 American Society for Mass Spectrometry.