Eric V. Dose

Comparison of the performances of overloaded elution and displacement chromatography for a given column

Abstract Using the semi-ideal model, chromatograms were calculated for the separation of a binary mixture on a given column by displacement and elution chromatography. The optimum conditions for the maximum production rate with or without a recovery yield constraint were determined using the simplex algorithm. Mixtures of relative retention 1.20 and 1.70 and relative composition 1:3 and 3:1 were considered. The maximum production rates achieved in both modes of chromatography are close. In all instances studied the ratio of the production rates of the two modes was between 0.5 and 2. Without a yield constraint, for the cases studied the recovery yield achieved in overloaded elution is much higher than that achieved in displacement chromatography. However, the concentration of the fraction collected in the displacement mode is one to two orders of magnitude higher than that of the fraction collected in the elution mode. The choice between the modes of operation will depend largely on the comparative economics of displacer recovery and fraction concentrations.

Peak Shape Distortions in the Capillary Electrophoretic Separations of Strong Electrolytes When the Background Electrolyte Contains Two Strong Electrolyte Co-Ions

A series of 25 mM phosphate buffer background electrolytes were prepared from phosphoric acid and mixtures of lithium hydroxide and tetrabutylammonium hydroxide as pH adjusters and sources of background electrolyte co-ions. These background electrolytes were used for the capillary electrophoretic separation of quaternary ammonium analytes. Abnormally distorted peaks, different from the simple characteristic triangular peaks usually attributed to electromigration dispersion, were observed. In order to understand the origin of the greatly distorted peaks, capillary electrophoretic separations with two co-ion background electrolytes were numerically simulated using a mathematical model of the electrophoretic process. Generalized peak shape rules were derived from the simulations which can be used to predict the shape of the analyte, co-ions, and counterion concentration peaks, as well as the local electric field strength changes. Abnormal peak shape and peak disappearance can occur when the analyte peak and the noncomigrating system peaks overlap.

Peak shape distortions during capillary electrophoretic separations of multicomponent samples in two co-ion buffers

Abstract During the capillary electrophoretic separation of a five-component quatternary ammonium analyte sample in two co-ion background electrolytes prepared from phosphoric acid, lithium hydroxide and tetrabutylammonium hydroxide, grossly distorted analyte peaks were observed. The electropherograms were successfully simulated using an earlier mathematical model of electrophoresis that was extended to handle up to eight nonprotic sample ions and two nonprotic background electrolyte co-ions. Peak shape distortion closely followed the predictions made during the recently described simulations of single analyte-two co-ion background electrolyte systems. Peak shape distortion was shown to depend on the relative mobilities of the particular analyte, the non-comigrating system peak and the governing co-ion. Severe peak shape distortion could occur in every multiple co-ion background electrolyte, such as in the indirect detection background electrolytes and charged interacting agent-containing background electrolytes, when certain analyte peaks and the non-comigrating system peaks overlap.