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

Abstract

Peak dispersion effects in nonaqueous capillary electrophoretic separations of aromatic anionic analytes were investigated in a propanolic background electrolyte solution. Poly(glycidylmethacrylate-co-N-vinylpyrrolidone) coating was applied to the capillary to suppress the electroosmotic flow and to improve the repeatability of the migration times. Electrical field strengths up to 2000 Vcm(-1) were applied in separations and the separation efficiencies were compared with theoretical values calculated on the basis of plate height theory. The contributions to the total plate height were calculated for injection plug length, diffusion, Joule heating, electromigration dispersion, analyte adsorption to the capillary wall, and detector slit aperture length. Analyte diffusion coefficients were measured by Taylor dispersion method, while distribution constants were measured chromatographically. Agreement between the calculated and empirical results was fairly good even though some approximations were required. In most cases the longitudinal diffusion contribution governed the total plate height, while the contribution of Joule heating was insignificant even at exceptionally high field strengths used. The relatively long detection slit aperture was found to influence the separation efficiency strongly, while the other dispersion sources that were investigated were of minor importance, except for adsorption in the case of one analyte. With all analytes, the dispersive effect of longitudinal diffusion was reduced as the field strength was increased, leading to enhanced migration velocities and faster separations.

Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussion

“…The variation will be compensated at least in part by the simultaneous variation of the velocity v, which includes the analyte mobility (see the discussion about the ratio m/D given above). The change of the rate constant of desorption, k d , upon substitution of one solvent by another is hard to predict (cf., e.g., [7,8] [34]). In general, the electrostatic interaction is thus enhanced in comparison to aqueous solutions, and the distribution constant is therefore increased.…”

“…Obviously, such data can be beneficial when planning the experimental setup, and is also valuable for the interpretation of the results obtained. In addition to MeOH and ACN other solvents, like ethanol (EtOH) [7], 1-propanol [8], propylene carbonate [9], N,N-dimethylformamide (DMF) [10], formamide (FA) [11], N,N-dimethylacetamide (DMA) [12], and nitromethane (NM) [13], have been applied to CE.…”

Band-broadening in capillary zone electrophoresis with axial temperature gradients

“…The resultant thermal plate height has been examined both theoretically and experimentally [19][20][21][22][23][24][25]. It was found that this thermal plate height is ordinarily small compared to that caused by molecular diffusion except at some extreme conditions [24,25].…”

“…Indeed, these authors observed concave-convex-concave fluid velocity profiles from the inlet to the outlet of the capillary [28]. Porras et al [14,15] and Palonen et al [24,25] studied the influence of solvent on the fluid temperature and the thermal peakbroadening in CZE at high electric fields. They obtained significantly low separation efficiency at high electric fields, which could not be explained by the radial temperature gradients induced thermal plate height.…”

“…21 in the forced air-cooling region [15,24,25]. T i in either the injection region or the detection region is always higher than " T i in the forced air-cooling region.…”