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Electrofocusing of Trace Contaminants

Jeffrey M. Burke and Cornelius F. Ivory. School of Chemical and Biological Engineering, Washington State University, Pullman, WA 99163

The analysis of impurities in pharmaceutically active compounds is becoming increasingly important as federal regulations become stricter. The most common technique for liquid phase analysis of contaminants is high performance liquid chromatography (HPLC). In general, however, only moderate resolution separations can be achieved and in many instances a prior concentrating technique is required for dilute samples. Isoelectric focusing (IEF), another commonly used liquid phase technique, separates and concentrates in the presence of a pH gradient and thus would not require a prior concentrating step. However, this technique requires that the analytes be amphoteric with an isoelectric point that is neither highly acidic nor highly basics. This is not always the case for pharmaceutics and thus could not be used for all samples. This paper discusses the use of dynamic field gradient focusing (DFGF) for the removal of trace contaminants from a desired product. DFGF is an additional electrofocusing method that can simultaneously separate and concentrate charged analytes in the presence of an electric field gradient. Unlike isoelectric focusing which separates in the presence of a pH gradient, DFGF does not require that the analytes be amphoteric, only that they have differences in their individual electrophoretic mobilites. In DFGF the electric field gradient is generated by a computer-controlled electrode array that allows for dynamic control and manipulation of the field profile during the course of an experiment to increase peak resolution, migrate analytes to off-take ports or to systematically elute individual species. Experimental results from the separation of two low molecular weight dyes, bromophenol blue and amaranth, at a concentration difference of 1000 fold are shown. These results along with a numerical simulation constructed in Comsol Multiphysics v3.4 are used to illustrate the potential of DFGF for trace contaminant analysis.