The effects of a mixture of charged and neutral additives on analyte migration behavior in capillary electrophoresis

Abstract

Multicomponent additives, such as derivatized cyclodextrins with various degrees of substitution, can be considered single-component additives as long as the fraction of each component remains constant. In this paper, equations are derived describing the effect of such additives on the migration behavior of analytes. These equations are used in the study of capillary electrophoresis (CE) systems with differentially charged cyclodextrins as additives. For weakly acidic analytes, the binding with highly negatively charged sulfobutyl ether beta-cyclodextrin (SBE-beta-CD) increases their negative electrophoretic mobility, while the binding with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) decreases their negative mobility. By obtaining the equilibrium constants and mobilities for each additive with each analyte (in this case, phenol, 2-naphthol and 1-naphthol), the migration behavior of these analytes in CE systems is quantitatively predicted at various concentrations of mixtures of the two additives. The properties of the contour lines in the binding isotherm surfaces of such CE systems are discussed.

Ultrashort partial‐filling technique in capillary electrophoresis for infinite resolution of tramadol enantiomers and its metabolites with highly sulfated cyclodextrins

“…Thus, experimental effective mobilities should be corrected for viscosity, temperature and ionic strength variations, which depend on variations of the chiral selector concentration and ionic strength. These corrections are crucial for an accurate determination of binding parameters [53].…”

Comprehensive strategy for chiral separations using sulfated cyclodextrins in capillary electrophoresis

“…As discussed in the Migration section, this is consistent with the theoretical development demonstrating that multicomponent additives in CE act as a weighted average of equilibrium and mobility behavior, and so can be treated as a single component if the relative amount of each component is constant. 35 Thus, the simple presence of different additives with different charges does not itself lead to variations in mobility and decreased separation robustness. However, if there is significant lot-to-lot variation for these random CDs that alters the fraction of each component in the mixture, then significant mobility variations can be expected between lots.…”

“…2 is a weighted average of the selector species present. 35 Analyte mobility, in this case, is a weighted average of the fraction of each selector species present. 35 If the relative composition of the mixture remains constant, Eq.…”

“…35 Analyte mobility, in this case, is a weighted average of the fraction of each selector species present. 35 If the relative composition of the mixture remains constant, Eq. 2 remains applicable and analyte migration is predicted to be unaffected by the mixed nature of the additive.…”

Generalized model of electromigration with 1:1 (analyte:selector) complexation stoichiometry: Part I. Theory

“…This equation has then become a basis for further method optimization in the dual-selector systems, predominantly in enantioseparations [25]. Similarly to the pH-overall model, Kranack et al [26] and later us [27] have shown that, effective mobility of an analyte (present in a single free form) interacting with a mixture of selectors can be expressed in a form of the S A S S Eq. (4):…”