QUANTITATIVE HYDROCARBON GROUP-ANALYSIS OF GASOLINE AND DIESEL FUEL BY SUPERCRITICAL FLUID CHROMATOGRAPHY

A two-dimensional supercritical fluid chromatographic system is described for the determination of saturates, alkenes and mono-, di- and tri-aromatics in gasoline and diesel fuel. Aromatics were isolated from saturates/alkenes and group separated according to the number of aromatic rings on a capillary column packed with silica of particle size 4-mu-m. The alkenes were separated from saturates on a 38-mm capillary column packed with a silica-based cation exchanger which had been modified in situ with silver nitrate. Elution of alkenes was facilitated by the use of a relatively high column temperature, 65-degrees-C, and operation in the back-flush mode. Carbon dioxide was used as the mobile phase. Relative standard deviations were generally in the range 0.4-20.0%. At a low content of alkenes, 0.5%, a relative standard deviation of 8.4% was achieved. The analysis time was under 8 min. The utility of the method is demonstrated by the analysis of feedstock before and after hydration.