Analysis of polycyclic aromatic hydrocarbons in kerogens using two-step laser mass spectrometry

Kerogen-bearing rocks from the Green River, Phosphoria, and Mowry formations 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 introduced into the instrument directly without pretreatment or processing. L2MS spectra were recorded from intact rocks and rock powder as well as from demineralized samples using a well established acid digestion procedure to isolate the kerogen. The main findings were as follows: (i) Spectra from demineralized samples and from pulverized rocks look almost identical. This similarity shows that grinding is sufficient as a sample preparation method for L2MS. Conventional acid digestion does not alter the PAH compositions of these samples. (ii) For immature and marginally mature samples, demineralization and grinding induce a change in the mass spectra compared to data taken from fracture surfaces of intact rock. This preliminary study shows the potential usefulness of L2MS for direct chemical analysis of complex materials such as kerogen; it may be useful to distinguish among kerogens of different maturities.