Calculation of the Hydrodynamic Contribution to Peak Asymmetry in High-Performance Liquid Chromatography Using the Equilibrium−Dispersive Model

Abstract

The equilibrium−dispersive model of chromatography and measurements of sorption isotherms were applied to reversed-phase C18 systems of several solutes with 40:60 methanol/water mobile phases to calculate the band shapes of eluites in the linear, analytical region of chromatography. These predicted profiles were compared to experimental profiles to determine the error associated with the equilibrium−dispersive model. This error is associated with the assumption of a uniform plug flow profile of mobile phase through the column. Analysis of the results of several systems and columns illustrates the asymmetry that exists in the actual mobile-phase flow profiles. The model error asymmetry decreases for higher efficiency columns as expected and increases in the form of peak tailing for lower efficiency columns. This behavior suggests that portions of the column are not swept by the mobile-phase flow at the same rate as the rest of the column, indicating an inhomogeneous packing density. The general method described is valuable for determining the relative contributions of thermodynamics and hydrodynamics to the peak asymmetry observed in liquid chromatography.

Investigation of the concentration dependence of mass transfer coefficients in reversed-phase liquid chromatography

“…Flow rate was 1.0 mL/min. The total porosity of the column, e T , was measured as 0.67 by using uracil as inner tracer [15]. The external porosity of the column, e e , was taken as a value of 0.375 from the literature which has been suggested by Kaczmarski et al [6] for the column packed with the particles of the same diameter.…”

“…As conventional use, FA can be used to accurately determine the adsorption isotherm [15,22]. Also, it has been proven to be an effective method to study the mass transfer kinetics in columns [13].…”

Evaluation of nonlinear chromatographic performance by frontal analysis using a simple multi-plate mathematical model

“…After each determination of the breakthrough curve, the column was washed with adequate methanol and then equilibrated with the mobile phase. Uracil was used as an inert tracer with methanol as mobile phase to determine the column void volume and extracolumn void volume [9].…”

“…If v 0 is taken as the retention value, the "saturation" of it shows that this value will be determined mainly by thermodynamics when Pe is large enough. This may be used to explain the reason of the success for the equilibrium model to predict the band profiles [7,9].…”

“…FA has been widely applied to determine adsorption isotherms from breakthrough curves that are obtained at different feed concentrations of the adsorbate [4][5][6][7][8][9]. As its inverse problem, the breakthrough curve may be predicted when the isotherm is already known.…”