GROUP-TYPE SEPARATION OF DIESEL FUELS USING PACKED CAPILLARY COLUMN SUPERCRITICAL-FLUID CHROMATOGRAPHY

Determination of the aromatic hydrocarbon content of diesel fuels by s upercritical fluid chromatography(SFC) has been approved as an America n Standard Test Method. Commercially available microbore columns usual ly used in this application suffer from poor stability and low resolut ion. In this work, 200 mu m i.d. packed capillary SFC columns were pre pared, and their chromatographic performances were compared with comme rcial microbore columns. Various packing materials with different pore sizes were evaluated, and the effects of column temperature and press ure were carefully examined. It was found that the pore size of the pa cking material and, therefore, the surface area had a significant effe ct on elution order. Using a 1 m long column, a resolution of as high- as 15 for n-hexadecane and toluene was achieved within 5 min at 45 deg rees C. The column performance was very reproducible; day-to-day and m onth-to-month resolution variations were less than 3%, and retention t ime variations were less than 1%. In this method, no additional column s and valve switching were involved. The method is simple, fast (simil ar to 10 min), and very suitable for quality control analysis.