FRACTIONATION OF SEDIMENTARY HIGHER-PLANT DERIVED PENTACYCLIC TRITERPANES USING MOLECULAR-SIEVES

Branched and cyclic alkane components of crude oil and sediments have been subjected to a liquid chromatography procedure in which a molecular sieve (ultrastable Y) was used as the stationary phase. n-Pentane was used as the mobile phase and the fractions eluted from the column were analysed using GC-MS techniques. The compositions of the first two fractions were markedly different to that of the initial branched and cyclic alkane mixture, especially when crude oils derived from higher-plant sources were used. In particular, the pentacyclic terpanes including bicadinanes, a spirotriterpane, oleananes and taraxastanes were enriched. Other compounds enriched in these fractions included the cadinanes and homocadinanes. Isolation of crude oil fractions enriched in pentacyclic alkanes using this procedure enabled lower concentrations of bicadinanes to be analysed than was previously possible by applying selective ion detection GC-MS techniques to branched and cyclic alkane fractions. Analysis of the fractions enriched in pentacyclic terpanes from an Indonesian crude oil revealed the presence of previously unreported C29 and C30 triterpanes. A comparison of mass spectral data, GC retention behaviours and molecular sieve sorption characteristics of these compounds with those of triterpanes of known molecular structure was used to suggest structures for the unknown compounds.