Estimation of vanadyl porphyrin concentration in sedimentary kerogens and asphaltenes

We describe a new, rapid method for determining the concentration of vanady l porphyrins (VO2+-P) associated with the kerogen of bituminous sedimentary rocks using electron spin resonance (ESR). The method is simple, straightf orward and inexpensive. Several concentrations of a vanadyl (VO2+) standard dissolved in glycerol-lignite mixture were prepared. The VO2+ concentratio ns ranged from 100 to 1000 ppm. The anisotropic ESR spectra of both the sta ndards and kerogen samples were recorded at room temperature and the integr ated areas of the pre-selected ESR line (attributed to nuclear spin m(t) = -5/2) were computed. The concentrations of VO2+ found in the kerogen sample s were calculated using the relative ratio of the integrated areas for the standards and the kerogen samples. The VO2+-P concentrations of the kerogen materials were then calculated using 350 as the mean molecular weight of t hese species. Quantitative determination of VO2+-P in the kerogen fractions in the range of 800-8000 ppm and higher is feasible by the method reported . The method of analysis was also extended to the asphaltene samples (enric hed with VO2+-P) and a coal sample containing non-porphyrin VO2+ associated with its organic fraction. (C) 2000 Elsevier Science Ltd. All rights reser ved.