Capillary supercritical fluid chromatography of explosives: Investigations on the interactions between the analytes, the mobile phase and the stationary phase

Abstract The independent effects of pressure and temperature in supercritical fluid chromatography on the capacity ratio on chromatographic resolution of some polar organic model compounds were investigated. Increasing the pressure isothermally leads to a steady decrease in retention and resolution. With changing temperature, a maximum in the capacity ratio as well as the resolution was observed. These observations may be related to a combination of gas chromatographic (GC) and liquid chromatographic (LC) theories of solute interactions with the mobile and stationary phases. However, pure GC- or LC-like behavior was not observed either below or above the critical point of the mobile phase. Capacity ratios for various explosives, propellants and related compounds were determined on capillary open tubular columns coated with either a non-polar methyl- or a polar cyanopropyl—phenyl-substituted siloxane stationary phase. The mobile phase for all studies was carbon dioxide. On the polar column, many of the solutes exhibited a good correlation between their bulk dipole moment and chromatographic retention. Deviations from this correlation could be explained by means of the physical or steric properties of these solutes. The elution order of the compounds on the non-polar column was similar to the order achieved using GC rather than LC.