Recent innovation in capillary electrokinetic chromatography with replaceable charged pseudostationary phases or additives

Abstract

Recent developments of separation of neutral analytes in capillary systems with the mobile phase driven by the electroosmotic flow (EOF) and charged additives acting as a pseudostationary phase are reviewed. As pseudostationary phases a number of additives are used. Soluble polymers, either anionic or cationic, were applied as alternatives to micelles. Monomeric charged additives are also intended to form associates with the analytes, leading to selective retention and separation in a similar way as the polymeric pseudostationary phases. Dendrimers, spherical macromolecules with highly branched chains and charged terminal groups, are successfully applied for the separation of lipophilic analytes. Polymers with covalently stabilized structures are introduced in the form of permanent micelles and are therefore insensitive to the mobile phase composition, enlarging the applicability of micellar electrokinetic capillary chromatography (MEKC).

Separation Methods for Toxic Components in Traditional Chinese Medicines

“…21 good separation of both charged and electrically neutral analytes. 80,81 Neutral compounds can be separated due to their different partition between the micelle and aqueous phase, and the separation mechanism of MEKC is a combination of both electrophoretic and chromatographic ability. In order to further realize the separation of some other toxic AA-related neutral components such as AL that can not be achieved by CZE method, we developed a MEKC method using sodium dodecyl sulfate (SDS) as surfactant.…”

Multiple effect of surfactants used as additives in background electrolytes in capillary zone electrophoresis: Cetyltrimethylammonium bromide as example of model surfactant

“…The use of micellar pseudostationary phases in MEKC are described in detail in a lot of references [23][24][25][26] and will not be discussed here. The CMC of CTAB in aqueous solution is low and can be even lower depending on ionic strength, pH, and temperature of the BGE.…”

“…(ii) Already at concentrations below the CMC, they interact selectively with sample analytes and BGE components, which, together with related changes in the EOF, are used to optimize the selective separation of analytes [7][8][9][10][11][12][13][14]. (iii) They change properties of the BGE such as the viscosity of the BGE solution, and they often create a pseudostationary phase, by using concentrations above the CMC and this is applied in micellar electrokinetic capillary chromatography (MEKC) ( [15, 16, for recent reviews see [17][18][19]). Obviously, the presence of a surfactant as an additive to a BGE always brings a complex situation where several effects are superimposed and mutually influenced.…”

Developments in the use of soluble ionic polymers as pseudo-stationary phases for electrokinetic chromatography and stationary phases for electrochromatography

“…The introduction and characterization of polymeric PSPs for EKC has been reviewed in detail [5][6][7]9,10]. Two reviews by this author in this journal concentrated on studies of the performance and selectivity of polymeric PSPs from their introduction in 1992 until 1997 [5,6].…”