Optimum conditions for preparative operation of capillary zone electrophoresis

The possibilities to use capillary zone electrophoresis (CZE) as a preparative tool have been studied, mostly from a theoretical point of view. The preparative performance of CZE is quantitated by the production rate, the amount of analyte that can be purified per unit of time. The production rate available with CZE is shown to depend in the first place on the chemical characteristics of the analyte-buffer combination. A figure of merit can be defined for a buffer system, describing its susceptibility to analyte overloading. Methods to find an optimal bufer system are referred to. It is shown that the loadability of the system is inversely proportional to the plate number required for the separation. A second important factor for the maximum production rate is shown to be the thermal management of the instrumental system. The average increase of the solution temperature and the non-uniform migration velocity by temperature differences within the solutions are discussed. It is shown that in practical cases the temperature rise of the solutions will be the main limiting factor when high fields are used. With low fields, which in general give a higher production rate, siphoning of the solution becomes the dominant limitation for the production rate. With cylindrical capillaries the highest production rate that can be obtained under practical conditions is in the order of 5.10 1 3 mol s -1. Experimental and theoretical results indicate that with rectangular capillaries the production rate can be increased by a factor of three.