Quantitative separation of aliphatic and aromatic hydrocarbons using silver ion-silica solid-phase extraction

A solid-phase extraction (SPE) method employing silver nitrate impregnated silica has been developed and evaluated for the separation of defined aliph atic and aromatic hydrocarbons from crude oils. The versatility of the SPE method is demonstrated using a light crude oh from the North Sea and a heav y crude oil from Orcutt field (Monterey, California, U.S.A). The coefficien ts of variation for a number of geochemical parameters measured on both ali phatic and aromatic hydrocarbons were excellent. The separation efficiency of SPE is demonstrated using quantification of monoaromatic steroid hydroca rbons which are notoriously difficult to efficiently sequester into the aro matic hydrocarbon fraction using traditional liquid chromatographic procedu re. The selectivity and efficiency of the SPE technique is comparable with that of silica gel TLC. However, losses of volatile compounds such as napht halene are limited during SPE since the sample remains in solvent. We concl ude that solid-phase extraction affords rapid sample turnover suitable for processing large sample numbers with high reproducibility.