INFLUENCE OF ANALYTE PLUG WIDTH ON PLATE NUMBER IN CAPILLARY ELECTROPHORESIS

A model of peak dispersion in capillary electrophoresis is proposed, In which the number N of theoretical plates is governed by longitudinal diffusion and the initial width of the analyte plug introduced into the capillary. To test the model, over 130 experimental determinations of N for dansyl-L-iso-leucine and several determinations of N for the marker of electroosmotic flow, acetone, were made for a variety of capillary lengths, voltages, and initial plug widths. The experiments were designed to reduce dispersion from other sources to acceptable levels. From experimentally determined values of mobility and current density, the buffer temperature In the capillary was determined at different field strengths. From this temperature, the apparent variations of analyte mobility and diffusion coefficient with field strength were determined and used in fitting experimental N's to the model. Peak shapes were predicted by additional theory to verify that only longitudinal diffusion and plug width affected N under the experimental conditions used here. On the basis of this study, it is argued that some anomalous values of N reported in the literature can be explained by this model, instead of Joule heating as previously argued.