Non‐uniform surface charge distributions in CE: Theoretical and experimental approach based on Taylor dispersion

Abstract

The control of the EOF direction and magnitude remains one of the more challenging issues for the optimization of separations in CE. In this work, we investigated the possibility to use non-uniform surface charge distribution for the modulation of the EOF in CE. Non-uniform zeta potentials were obtained by modifying a section of the capillary surface using adsorption of polyelectrolytes. Three different methods were studied: (i) partial polycation coating on a fused silica capillary, (ii) partial polycation (or polyanion) coating on polyelectrolyte multilayers, and (iii) partial polycation coating on a capillary previously modified with poly(ethylene oxide). The magnitude and the direction of the EOF as a function of the coated capillary length were first studied. The stability of the EOF and the separation performances were also considered taking two dialanine diastereoisomers as model compounds. In partially coated capillaries, the average solvent flow is the sum of two contributions: a non-dispersive electroosmotic contribution related to the capillary surface charge, and a dispersive hydrodynamic contribution that depends on the difference of surface charge between the coated and the non-coated capillary zones. To get a better insight into the influence of the hydrodynamic contribution to the total peak dispersion, the peak variances corresponding to the Taylor dispersion, the injection plug, and the axial diffusion were calculated. This work demonstrates that peak dispersion in a capillary partially coated by the inlet end is different from that obtained when the coating is performed by the outlet end. Experimentally, the combination of a partially coated capillary with a large volume sample stacking preconcentration step can be used for injecting up to 95% of the capillary volume. This approach leads to a preconcentration factor of 60 compared with CZE with classical injection.

Sequence requirements of oligonucleotide chiral selectors for the capillary electrophoresis resolution of low‐affinity DNA binders

“…It is also important to notice that, in these experimental conditions, the maximal oligonucleotide injection volume cannot exceed 50% of the total volume of the capillary otherwise the oligonucleotide plug moves toward the outlet side of the capillary (toward the detector) even though the conductivity is the same in both compartments (BGE1 compartment and ON compartment). It is well known that in the presence of two different zones, in a bare‐fused silica capillary, the average solvent flow is equal to the average of the electroosmotic mobilities of each zone, weighted by the relative lengths of the zones . Then, we can assume that the electroosmotic mobility in ON compartment is higher than the electroosmotic mobility in the BGE1 compartment.…”

Use of coated capillaries for the electrophoretic separation of stereoisomers of a growth hormone secretagogue

“…The use of charged polyelectrolytes for capillary coating has become popular in CE, especially for peptides and proteins analysis to prevent analyte adsorption [43][44][45][46][47][48][49][50] and to control the EOF [51][52][53][54]. The polyelectrolytes are generally highly adsorbed to the capillary via electrostatic, hydrogen and even hydrophobic interactions [10,17,18,22,23,[55][56][57].…”

Contemporary sample stacking in analytical electrophoresis

“…The authors 43 investigated the possibility to use nonuniform surface charge distribution for the modulation of the EOF in CE. They found that the combination of a partially coated capillary with a LVSS preconcentration step can be used for injecting up to 95% of the capillary volume.…”