Retention characteristics in supercritical fluid chromatography and comparison with gas chromatography

A practical method for the characterization of the retention behavior in su percritical fluid chromatography (SFC) was proposed, based on the retention index. Taking easier comparison with gas chromatography (GC) into consider ation, a set of six test compounds were chosen: napthalene, 1-pentadecanol, 2-pentadecanone, n-pentadecanonitrile, isoquinoline and cyclododecane. Dim ethylsilicone and carbon dioxide were selected as the standard stationary p hase and the standard mobile phase, respectively. Thus, the differences in retention indexes for the test compounds between the SFC conditions in ques tion and the standard SFC conditions, i.e., the Delta I values, were used f or the expression of the retention characteristics, similarly to use of the McReynolds constants in GC. The difference or similarity of retention beha vior could be evaluated by the angle between two vectors having six element s, which corresponded to two SFC conditions. This method could detect the s mall difference in the retention behavior on a slightly polar Stationary ph ase: 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.