Retention Characteristics in Supercritical Fluid Chromatography and Comparison with Gas Chromatography

Abstract

A practical method for the characterization of the retention behavior in supercritical fluid chromatography (SFC) was proposed, based on the retention index. Taking easier comparison with gas chromatography (GC) into consideration, a set of six test compounds were chosen: napthalene, 1-pentadecanol, 2-pentadecanone, n-pentadecanonitrile, isoquinoline and cyclododecane. Dimethylsilicone and carbon dioxide were selected as the standard stationary phase and the standard mobile phase, respectively. Thus, the differences in retention indexes for the test compounds between the SFC conditions in question and the standard SFC conditions, i.e., the ΔI values, were used for the expression of the retention characteris-tics, similarly to use of the McReynolds constants in GC. The difference or similarity of retention behavior could be evaluated by the angle between two vectors having six elements, which corresponded to two SFC conditions. This method could detect the small difference in the retention behavior on a slightly polar stationary phase: 50% methyl, 50% phenylsilicone between GC and SFC. This difference was attributed to the different behavior of cyclic compounds from that of non-cyclic compounds.