ANALYSIS OF POLYCYCLIC AROMATIC-HYDROCARBONS IN KEROGENS USING 2-STEPLASER MASS-SPECTROMETRY

Kerogen-bearing rocks from the Green River, Phosphoria, and Mowry form ations were analyzed for polycyclic aromatic hydrocarbons (PAHs) using two-step laser mass spectrometry (L2MS). This method allows sensitive analyses to be carried out within minutes, and samples can be introdu ced into the instrument directly without pretreatment or processing. L 2MS spectra were recorded from intact rocks and rock powder as well as from demineralized samples using a well established acid digestion pr ocedure to isolate the kerogen. The main findings were as follows: (i) Spectra from demineralized samples and from pulverized rocks look alm ost identical. This similarity shows that grinding is sufficient as a sample preparation method for L2MS. Conventional acid digestion does n ot alter the PAH compositions of these samples. (ii) For immature and marginally mature samples, demineralization and grinding induce a chan ge in the mass spectra compared to data taken from fracture surfaces o f intact rock. This preliminary study shows the potential usefulness o f L2MS for direct chemical analysis of complex materials such as kerog en; it may be useful to distinguish among kerogens of different maturi ties.