Predicting peak symmetry in capillary zone electrophoresis.: Background electrolytes with two co-ions:: Schizophrenic zone broadening and the role of system peaks

This paper investigates fundamental phenomena in the migration behavior of analytes in the very frequent case in current capillary zone electrophoresis practice of using background electrolytes with two co-ions. It is shown that in such background electrolyte systems there always exists a regular system phenomenon which brings enormous electromigration dispersion to certain analytes. The analytes which yield to this phenomenon may be predicted by calculating the so-called velocity slope Sr, which is a measure of zone symmetry and broadening. On the example of a simplified model system, it is shown explicitly that these analytes coincide by their mobilities with the mobility of the system peak. The explanation for these effects is given on the basis of schizophrenic behavior where one and the other co-ions force the analyte zone to be fronting and tailing simultaneously. Detailed theoretical description of the behavior of analyte zones in binary co-ion background electrolytes is presented using peak shape diagrams that provide a comprehensive view of their electromigration dispersion characteristics. Experimental verification of the theory is given, together with a detailed discussion of the effect of the background electrolyte composition on the magnitude and extent of appearance of schizophrenic zone broadening.