Novel cationic polyelectrolyte coatings for capillary electrophoresis

The use of bare fused silica capillary in CE can sometimes be inconvenient due to undesirable effects including adsorption of sample or instability of the EOF. This can often be avoided by coating the inner surface of the capillary. In this work, we present and characterize two novel polyelectrolyte coatings (PECs) poly(2-(methacryloyloxy)ethyl trimethylammonium iodide) (PMOTAI) and poly(3-methyl-1-(4-vinylbenzyl)-imidazolium chloride) (PIL-1) for CE. The coated capillaries were studied using a series of aq. buffers of varying pH, ionic strength, and compn. Our results show that the investigated polyelectrolytes are usable as semi-permanent (phys. adsorbed) coatings with at least five runs stability before a short coating regeneration is necessary. Both PECs showed a considerably decreased stability at pH 11.0. The EOF was higher using Good's buffers than with sodium phosphate buffer at the same pH and ionic strength. The thickness of the PEC layers studied by quartz crystal microbalance was 0.83 and 0.52 nm for PMOTAI and PIL-1, resp. The hydrophobicity of the PEC layers was detd. by anal. of a homologous series of alkyl benzoates and expressed as the distribution consts. Our result demonstrates that both PECs had comparable hydrophobicity, which enabled sepn. of compds. with log Po/w > 2. The ability to sep. cationic drugs was shown with β-blockers, compds. often misused in doping. Both coatings were also able to sep. hydrolysis products of the ionic liq. 1,5-diazabicyclo[4.3.0]non-5-ene acetate at highly acidic conditions, where bare fused silica capillaries failed to accomplish the sepn.