Nonlinear liquid chromatography linear isotherm

With binary and ternary supercritical mixtures as chromatographic mobile phases, solute retention mechanisms are unclear. Polar modifiers produce a nonlinear relationship between the log of solute partition ratios (k ) and the percentage of modifier in the mobile phase. The only form of liquid chromatography (LC) that produces non-linear retention is liquid-solid adsorption chromatography (LSC) where the retention of solutes follows the adsorption isotherm of the polar modifier (6). Recent measurements confirm that extensive adsorption of both carbon dioxide (7,8) and methanol (8,9) occurs from supercritical methanol/carbon dioxide mixtures. Although extensive adsorption of mobile phase components clearly occurs, a classic adsorption mechanism does not appear to describe chromatographic behavior of polar solutes in packed column SFC. [Pg.137]

Interaction between adjacent adsorbed sample molecules (2) as a contribution to isotherm nonlinearity is relatively unimportant, particularly in liquid-solid chromatography. These interactions are normally possible "fenly at relatively high surface coverages, where linearity is already limited by surface saturation [Eq. (4-1)] and by adsorbent heterogeneity. Furthermore, interactions between adsorbed sample molecules are largely canceled... [Pg.44]