Contribution of capillary coiling to zone dispersion in capillary zone electrophoresis

A mathematical model of the deformation of the analyte zone in capillary zone electrophoresis (CZE) due to capillary coiling is presented and the influence of capillary coiling on the distribution of electric current density inside the capillary is described. The model gives a quantitative description of the potential contribution of capillary coiling to the total zone dispersion in CZE. The zone broadening caused by capillary coiling is calculated as the difference of migration distances of the particles migrating at the inner circumference of the capillary coil and those migrating at the outer circumference. This difference is shown to be directly proportional to the capillary diameter and to the number of capillary coils, i.e. indirectly proportional to the radius of the capillary coils into which the capillary of the given length is coiled. The contribution of capillary coiling to the total zone dispersion is compared with the contribution of the longitudinal diffusion of low and high molecular mass analytes and bioparticles. It is shown that, especially in the case of CZE separation of macromolecules and particles, capillary coiling can significantly decrease the separation efficiency. For that reason the small radius coiling of the capillary column in the CZE apparatuses should be avoided.