Stochastic simulation of reactive separations in capillary electrophoresis

A dynamic molecular probe to investigate catalytic effects and Joule heating in enantioselective MEKC

Enantiomerization of ferroin [tris(1,10-phenanthroline)-iron(II)-complex] was investigated by enantioselective dynamic micellar EKC. The enantiomer separation was performed in an aqueous 50 mM sodium borate/sodium dihydrogenphosphate buffer at pH 8.0 in the presence of the chiral surfactant sodium cholate. The unified equation of dynamic chromatography was employed to determine reaction rate constants from the electropherograms featured with distinct plateau formation. Activation parameters DeltaH( not equal) = 124.0 +/- 0.5 kJ/mol and DeltaS( not equal) = 121 +/- 1 J.K(-1)mol(-1) were calculated from temperature-dependent measurements between 10.0 and 27.5 degrees C in 2.5 K steps. Considering the data obtained by polarimetry of enantiomeric pure ferroin in water, it was found that enantiomerization rate in the micelle is accelerated by a factor of 12. Because of the highly positive activation entropy DeltaS( not equal), ferroin was used as a temperature-sensitive dynamic molecular probe to determine temperature deviations caused by Joule heating.

Capillary electrophoresis for thermodynamic and kinetic studies of peptidyl-proline isomerization by the theoretical plate height model

The theoretical plate height model, extended to include reactive CE, is used to calculate equilibrium constants and rate constants for the reversible, first-order isomerization of proline dipeptides. This model is consistent with chromatographic theory and enables calculation of equilibrium constants from velocity and calculation of rate constants from plate height. Thermodynamic and kinetic parameters for isomerization of Ala-Pro and Phe-Pro are calculated by using the plate height model, and are shown to be in good agreement with literature values. Additionally, the efficacy of the plate height model is compared to ChromWin, an existing simulation method for calculating rate constants from zone profiles. It is shown that ChromWin and the plate height model are complementary methods. ChromWin is best used for calculating rate constants for reactions that are far from steady state, where the zone profiles exhibit plateau formation. On the other hand, the plate height model is best used for calculating rate constants for reactions that are at or near steady state, where the zone profiles exhibit a single zone containing both reacting species.

Effects of nonequilibrium on velocity and plate height in reactive capillary electrophoresis

Models for velocity and plate height for reactive CE are developed under the formalism of generalized nonequilibrium theory, as described by Giddings. The resultant equations are consistent with chromatographic theory and validated with an independent stochastic simulation. Moreover, unlike prior methods for CE, this model allows calculation of thermodynamic equilibrium constants and kinetic rate constants from a single, undistorted peak. The theoretical development shows that velocity is directly dependent on the equilibrium constant and is independent of the rate constant. On the other hand, plate height varies little with equilibrium constant and is inversely proportional to rate constant. The ability to evaluate equilibrium constants from velocity and rate constants from plate height is most greatly influenced by electric field strength and mobility difference. The accuracy in calculated equilibrium constants is limited by mobility difference; however, the accuracy in rate constants is limited by plate height and equilibrium constant.