Characteristics of sulfolane as a novel stationary phase in supercritical fluid chromatography

Sulfolane (C 4 H 8 SO 2 ) is a small, polar, aprotic, cyclic molecule largely used as a solvent in oil and gas production for its interesting selectivity towards aromatic compounds. Here, sulfolane is examined as a novel stationary phase for use in capillary column supercritical fluid chromatography with flame ionization detection (SFC-FID). A 2 m × 250 µm stainless steel capillary was found to be optimal for retaining the sulfolane phase and achieving practical retention times for most analytes. Under typical conditions of 65 °C and 120 atm, the dynamic solubility of sulfolane in the supercritical CO 2 mobile phase was measured to be only 0.6 g/L. This translated into minimal system detector noise for various mobile phase pressure and temperature settings that produced a moderate CO 2 density of 0.4 g/mL or lower. In this way, the phase normally provided good performance and very little background interference in the FID over several hours of operation. Due to its thickness (∼4 µm) the phase produced plate heights about 10-fold larger than optimal capillary SFC performance, but with an elevated sample capacity near 50 µg of injected analyte. Good retention and peak shape were obtained for various polar and non-polar analytes. Conversely, organic acids and bases yielded poor peak shape and low recovery on the column. Adding water to the sulfolane coating produced significant changes in analyte selectivity. Compared to a longer conventional SFC column, the relatively short sulfolane column demonstrated high selectivity towards aromatic analytes over saturates in the analysis of a gasoline sample. Results indicate that sulfolane might be a potentially useful alternative stationary phase for the selective SFC analysis of aromatics in various petroleum samples.