RETENTION IN SUPERCRITICAL FLUID CHROMATOGRAPHY ON CYANO-BONDED SILICA COLUMNS

The factors affecting the retention of analytes in supercritical fluid chromatography on cyano-bonded silica columns have been examined by using a homologous series of alkyl aryl ketones and selected aromatic test compounds. Carbon dioxide or methanol-modified carbon dioxide was used as the mobile phase. The retentions of the homologous ketones were consistent with a combination of the normal-phase interactions of the analytes with the polar stationary phase and their volatility. For the test compounds the primary influence appeared to be polar interactions with the free silanol groups on the stationary phase, which were greatly reduced by the addition of methanol to the mobile phase. There were significant differences in the retention properties of four different brands of cyano-bonded stationary phase, which could be related to the extent of coverage of the silica surface.