An Analogue Column Model for Nonlinear Isotherms. The Double-Glazed Vessel Model.

Abstract

The "double-glazed vessel model" (DGV model) is an imaginary model modified from the previously reported "test tube model", and is drawn graphically by computer. The vessel has a double wall, the inner wall of which has a pinhole near the bottom. The "mass of gathered solute molecules" is considered to be liquid, and is referred to merely as "solute". At equilibrium, the solute levels in the two compartments become equal. The inner and outer compartments form the shapes of solute in the stationary and mobile phases, respectively. For example, a vessel with cylindrical (inner) and trumpet-shaped (outer) walls is devoted to the convex (Langmuir-type) isotherm. Computer simulations of chromatography using the DGV model directly explained the asymmetric peaks caused by nonlinear isotherms. For example, the explanation of the tailing peak caused by convex isotherm, "as much solute is transferred (relatively to that remaining in the stationary phase) at the center of the band rather than at the edges, i.e. as the center moves faster than the edges, the chromatogram exhibits tailing", is directly understood from the simulated result ( Figure 4A).