Characterization of polycyclic aromatic hydrocarbon minerals curtisite, idrialite and pendletonite using high-performance liquid chromatography, gas chromatography, mass spectrometry and nuclear magnetic resonance spectroscopy

Abstract

Two polycyclic aromatic hydrocarbon (PAH) minerals — curtisite and idrialite — have been characterized using high-resolution gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) with fluorescence detection. Normal-phase HPLC on an aminosilane column was used to separate the mineral extracts into six fractions based on the number of aromatic carbon atoms in the PAH. These fractions were then analyzed by using GC-MS and reversed-phase HPLC with fluorescence detection to separate and identify the individual components. One fraction was also analyzed by using nuclear magnetic resonance spectroscopy to provide structural information and information on the position of alkyl-substitution. Using these analytical techniques, the curtisite and idrialite were found to be unique complex PAH mixtures consisting of six specific PAH structural series with each member of a series differing from the previous member by addition of another aromatic ring. The curtisite and idrialite samples contained many of the same components but in considerably different relative amounts. The major PAH constituents of the curtisite sample were: picene, dibenzo[ a,h]fluorene, 11H-indeno[ 2,1-a]phenanthrene, benzo[ b]phenanthro[2,1-d]thiophene, indenofluorenes, chrysene, and their methyl- and dimethyl-substituted homologues; the major components in the idrialite sample were higher-molecular-weight PAH, i.e. benzonaphthofluorenes (molecular weight 316), benzoindenofluorenes (MW 304) and benzopicene (MW 328), in addition to the compounds found in the curtisite sample. The combination of HPLC to isolate specific PAH groups and the analysis of these fractions by HPLC-fluorescence and GC-MS resulted in the positive identification of ∼ 20 of the over 100 PAH found in these two samples. The identification of these compounds supports the conclusions of M. Blumer that these minerals were formed by medium-temperature pyrolysis of organic compounds, followed by extended equilibration at elevated temperatures in the subsurface.