Affinity capillary electrophoresis: the theory of electromigration

Abstract

We focus on the state-of-the-art theory of electromigration under single and multiple complexation equilibrium. Only 1:1 complexation stoichiometry is discussed because of its unique status in the field of affinity capillary electrophoresis (ACE). First, we summarize the formulas for the effective mobility in various ACE systems as they appeared since the pioneering days in 1992 up to the most recent theories till 2015. Disturbing phenomena that do not alter the mobility of the analyte directly but cause an unexpected peak broadening have been studied only recently and are also discussed in this paper. Second, we turn our attention to the viscosity effects in ACE. Change in the background electrolyte viscosity is unavoidable in ACE but numerous observations scattered throughout the literature have not been reviewed previously. This leads to an uncritical employment of correction factors that may or may not be appropriate in practice. Finally, we consider the ionic strength effects in ACE, too. Limitations of the current theories are also discussed and the tasks identified where open problems still prevail. Graphical Abstract A weak base (A) undergoes an acidic-basic equilibria (in blue) and migrates with an electrophoretic mobility of [Formula: see text]. Simultaneously, it interacts with a selector (sel) while the analyte-selector complex migrates with an electrophoretic mobility of [Formula: see text]. The strength of the interaction (in orange) is governed by the binding constant, K , and the concentration of the selector, c . This all gives the analyte an effective mobility of [Formula: see text] and moves it out of the zero position (EOF; right top insert). The interaction of the positively charged analyte with the neutral selector slows down the analyte with increasing selector concentration (right bottom insert).

Enhancement of the conductivity detection signal in capillary electrophoresis systems using neutral cyclodextrins as sweeping agents

“…Quirino and Terabe expressed a sweeping factor in micellar electrokinetic chromatography (MEKC) by means of the analyte‐micelles partitioning equilibria and the equation was later adopted to MEKC systems with neutral micelles , too. We show elsewhere that this approach is valid only if the selector electrophoretic mobility is not affected by the complexation, an assumption generally accepted in MEKC. Later, the authors re‐applied their derivation in a system with a neutral analyte and borate as a sweeping agent .…”

Generalized model of the linear theory of electromigration and its application to electrokinetic chromatography: Theory and software PeakMaster 6—Next Generation

“…Section 2.1) allows us to reformulate LTEM to cover electrophoretic systems comprising any chemical equilibrium so that equilibrium reactions are fast enough to instantaneously reach equilibrium. In practical terms, the time scale of every reaction is negligible in comparison with that of the separation process (notice that the latter is measured as the time needed for a peak to travel the peak width, and not as the time of the entire separation ). Therefore, at any time and position in the capillary, the concentration of every form can be expressed as an algebraic function of concentrations of all constituents …”

Computer simulation of the enantioselective separation of weak bases in an online capillary electrophoresis based microanalysis configuration comprising sulfated cyclodextrin as selector

“…Thus, electrophoresis proceeds in a discontinuous buffer system . The discontinuities of the buffer system are accompanied by changes in pH, conductivity, and ionic strength, in which the latter has a large impact on chiral separations by influencing the effective mobilities of all components, and potentially also the values of binding constants . The electrophoretic processes occurring in this complex system are herein described utilizing computer simulation with the software SIMUL5complex.…”