MIGRATION BEHAVIOR MODELING OF ANIONIC SPECIES IN A HYDROORGANIC BACKGROUND ELECTROLYTE

The migration of benzoate derivatives in a hydroorganic background electrolyte (BGE) was predicted using a novel mathematical model. In capillary electrophoresis (CE), with an acetonitrile (ACN)/buffer mixture as BGE, the influence of pH and the ACN cluster fraction can be quantitatively described by a general equation which was used to study the separation optimization. The cluster solute solvation energies in an ACN/buffer mixture over a 0.50–0.80 buffer fraction were calculated. The energetics of the ACN cluster exchange process in the BGE was investigated in relation to the difference in pKa (ΔpKa) between a solute used as reference and the other solutes. A linear correlation was found between the Gibbs free energy change of the solvent exchange process and ΔpKa confirming that the solute solvation by ACN clusters was enhanced for the lesser polar solutes. Enthalpy-entropy compensation revealed that the solute solvation mechanism was independent of both the benzoate derivative structure and the BGE ionic strength.

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