Contribution of capillary coiling to zone dispersion in capillary zone electrophoresis

Abstract

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.proportiona1 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. Nonstandard abbreviations: BGE, background electrolyte; HETP, height equivalent of theoretical plate

Peak broadening in microchip electrophoresis: A discussion of the theoretical background

“…This is the reason of designing microchip systems often by folding separation channels into meanders and other shapes with turns. The detrimental effect of capillary coiling was noticed earlier [6] and it was approximately accounted for the excess dispersion [7] in the cylindrical channel, which proved that this effect is far from being significant in classical capillary electrophoresis. The complicated geometry of the microchip channels having turns with a smaller radius brought new queries to solve these problems in full details.…”

Number of theoretical plates achievable by a toroidal capillary electrophoresis system

“…To calculate the plate number ( N ) for this TCE format with four reservoirs, the following equation is used: N = L 2 /σ 2 , where L is the total distance run by the analyte in the reference frame of the buffer solution or organic solvent and σ is the spatial SD of the band distribution along the axial direction of the toroid at the end of the run. The effect of capillary bending (to produce the toroid) on the band broadening will be neglected, as this is negligible for the dimensions studied here (for instance a toroid with L t = 100 cm and 50 μm id) . Carefully conducted experiments exhibit only diffusion as a significant band broadening mechanism.…”

Peak dispersion and contributions to plate height in nonaqueous capillary electrophoresis at high electric field strengths: Ethanol as background electrolyte solvent

“…The simple analytical model used allows calculation of the contributions of various dispersion sources to the total plate height, and from these, evaluation of the main dispersion sources involved in separation. The contributions of EOF profile [31] and capillary coiling [32] to the total plate height were ignored, because they are not significant in our experimental setup. Also hydrodynamic effects [33] were omitted from the model, because the capillaries used were very narrow and effects such as siphoning (see, e.g., [34,35]) do not play a significant role provided that the liquid levels at both ends of the capillary are balanced.…”