Role of chemical equilibria in the capillary electrophoresis of inorganic substances

Electrophoretic behaviour of low-molecular-mass substances and their separa tion can be effectively manipulated employing selective interactions betwee n the separated ions and components of working solutions. Proper selection of operational electrolytes can considerably enhance the selectivity of ele ctrophoretic separations without expensive modifications of instrumentation . Complex-forming acid-base and ion association equilibria are most importa nt for influencing the effective mobilities of inorganic cations and anions . These can be used for optimization of separations. On the other hand, cap illary electrophoretic methods can be used for investigations of chemical e quilibria and measurements of physicochemical characteristics, such as stab ility, dissociation/protonation, ion association, etc., constants. Formatio n of complexes of the separated ions with suitable ligands contained in the working solutions is especially useful in the case of the capillary electr ophoretic determination of metals (transition and heavy metals, rare earth elements). As can be seen from ct number of published operational systems, similar complexing agents are used in various electrophoretic modes, namely in capillary zone electrophoresis (CZE) and in capillary isotachophoresis (ITP). Hence the previously described systems for ITP separations can serve as an inspiration in the course of the development of new CZE methods. (C) 1999 Elsevier Science BN. All rights reserved.