Supercritical fluid chromatographic determination of hydrocarbon groups in gasolines and middle distillate fuels

A supercritical fluid chromatographic method to determine the percentage of saturates, olefins, and aromatics in gasolines and middle distillate fuels was developed. A microbore (1 mm i.d.) silica gel column was used to isolate and determine the aromatics, while a silver-ion-loaded strong cation exchange silica gel microbore column was used to separate the saturates from the olefins and aromatics. Olefins were determined by difference or by using a column switching technique which allows complete separation of saturates, olefins, and aromatics in a single run. A mixed mobile phase of 10% CO/sub 2/ in SF/sub 6/ (mole percent) was used for both columns, and a flame ionization detector provided uniform, linear response of the hydrocarbons, allowing quantitation with minimal calibration. The average absolute error was 1.5%, while the standard deviation of the area percent of the aromatics of one gasoline sample was 0.5%. Analysis times of under 60 min were achieved.