CHARACTERIZATION OF FUELS BY MULTIDIMENSIONAL SUPERCRITICAL-FLUID CHROMATOGRAPHY AND SUPERCRITICAL-FLUID CHROMATOGRAPHY MASS-SPECTROMETRY

A multi-dimensional supercritical fluid chromatographic (SFC) system was evaluated for the determination of saturated compounds, alkenes, mono-, di- and triaromatics and polar compounds in diesel fuel distillates. The system consisted of three packed microcolumns, which were packed with cyano-modified silica, silica and in situ silver ion-impregnated cation exchanger. Further, an interface for SFC-electron impact MS was constructed. The application of direct fluid introduction was possible when packed microcolumns of 50 mum I.D. were employed. The different groups of organic compounds were readily separated, with the exception of alkanes/alkenes and monoaromatics. This separation became increasingly incomplete as the boiling range of the distillates was increased. Using SFC-MS, it was found that the lack of baseline separation depended solely on the tailing of the alkane/alkene peak. However, for most diesel distillates, only a minor part of the alkane/alkene peak co-eluted with the monoaromatics. In addition, examination by SFC-MS provided data for the proper selection of integration limits. The determination of aromatics was in good agreement with the results obtained using the HPLC method IP 391/90.