Comparison of titania, zirconia, and silica stationary phases for separating diesel fuels according to hydrocarbon group-type by supercritical fluid chromatography

Silica, zirconia, and titania columns were compared for their ability to separate diesel samples into saturates, mono-, di-, tri-, and polyaromatics by supercritical fluid chromatography (SFC) using pure CO2 according to ASTM method D 5186-03. A titania column coupled in series to a silica column was found to provide the highest overall group-type resolutions based on 20 model compounds, with resolutions as high as 14.7 for saturates versus monoaromatics and 11.9 for monoaromatics versus diaromatics. An oilsands-derived Synfuel light diesel, a commercial Ontario diesel, and a heavy Shell Canada Ltd. diesel blending feedstock were studied on a titania–silica coupled column as well as on a conventional silica column. The Synfuel results were similar (within 0.5 mass%) on both the conventional bare silica column and the titania–silica coupled column. The heavier commercial diesel and diesel blending feedstock samples yielded different results on the titania–silica coupled column compared to the silica column alone, demonstrating the importance of achieving the highest possible resolutions when baseline separation of group-types is not obtained.