Packed Capillary Column Chromatography with Gas, Supercritical, and Liquid Mobile Phases

Introduction The concept of unified chromatography was defined by Giddings over thirty years ago, when he pointed out (1) that there are no distinctions between chromatographic separation modes which are merely classified according to the physical state of the mobile phase (GC, SFC and HPLC). Recently, Chester has described (2) how a consideration of the phase diagram of the mobile phase shows that a one-phase region (Figure 1) is available for the setting of mobile phase parameters, and that the boundaries separating individual techniques are totally arbitrary. By varying pressure, temperature and composition, solute - mobile phase interactions can be varied so as to permit the chromatographic elution of analytes ranging from permanent gases to ionic compounds; the dependence of solute diffusion coefficient in the mobile phase on pressure, temperature and composition, (Figure 1) also influences mass-transfer characteristics and also has an important bearing on the choice of an appropriate