Gas-Chromatographic Mass-Spectrometric Studies on the Isoprenoids and Other Isomeric Alkanes in Meteorites

Abstract

A detailed study of a number of hydrocarbons observed in gas chromatographic analyses of six carbonaceous chondrites (Essebi, Grosnaja, Mokoia, Murray, Orgueil, and Vigarano) has resulted in the identification of nine homologous series of isomeric alkanes in addition to the normal alkane series. Two of them show isoprenoid structures corresponding to 2, 6, 10-trimethyl and 2, 6, 10, 14-tetramethyl alkanes. The individual members identified in each of these two series cover the ranges C14-C19 and C19-C21, respectively. The rest is made up of five series of monomethyl alkanes (6-, 5-, 4-, 3-, 2-methyl alkanes) and two of monocycloalkanes (cyclohexyl and cyclopentyl). The presence of members of the n-paraffin series between C11 and C21 inclusive was also confirmed by mass spectral data. The hydrocarbon content ranged from 6.7 to 82.8 ppm.An identical study of the graphitetroilite nodules of three iron meteorites yielded results qualitatively very similar to the carbonaceous chondrites. The hydrocarbons range in this case from 0.32 to 9.36 ppm. Five homologous series have been identified mass spectrometrically: the n-alkane series (C13 to C26); the 2-, 3-, 4-, 6-methyl alkane series; and the two isoprenoid series, 2, 6, 10-trimethyl and 2, 6, 10, 14-tetramethyl alkanes (C16-C19 and C19-C21, respectively). Two series of monocycloalkanes (cyclohexyl and cyclopentyl) have also been found. The more internal parts of the nodules show (1) smaller amounts of hydrocarbons (from 3–7 times less than the surface), and (2) an increase in the ratio of isoprenoids to normal alkanes.Isoprenoids are present in all meteoritic samples analyzed. Usually they show a major maximum at C19 (pristane) and a secondary maximum at C16 (methyl farnesane) with a minimum at C17. Comparative studies of isoprenoid distributions typical of meteorites show a much greater degree of correlation with their distributions in sediments and petroleum crudes than with those produced by continuous flow Fisher-Tropsch processes.KeywordsHomologous SeriesCarbonaceous ChondriteGraphitic NoduleIron MeteoritePetroleum CrudeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.