Analysis of factors causing peak broadening in capillary zone electrophoresis

Abstract An equation analogous to the Van Deemter equation in chromatography is developed to account for peak broadening in capillary zone electrophoresis (CZE). This equation applies to conditions wher the peaks are symmetrical (sample zone concentration much less than background electrolyte concentration). To identify and to quantitate the effects of different contributions to the peak width in CZE, it is first necessary to put all peak profiles on the same footing by correcting them for the velocities fo different zones and for the finite length of the detector zone compared to the sample zone. Three major contributors to the peak width are identified: (1) the injection length of the sample; (2) longtudinal diffusion that takes place during the migration time between injection and detection; and (3) analyte-wall interactions. Temperature is shown not to be a major factor in peak broadening under typical experimental conditions. The predictions of our model agree well with experimentally determined peak profiles for different analytes under a variety of conditions. New expressions for theoretical plate number and resolution in CZE are presented. It is concluded that in almost all previously reported CZE separations the peak profiles were dominated by the sample injection length. This explains why the observed peak widths in CZE have been broader than anticipated.