Prediction and optimization of the separation of metal cations by capillary electrophoresis with indirect UV detection.

The migration of metal cations in capillary electrophoresis with indirect UV detection was investigated. A mathematical model was used to relate the electrophoretic mobility of a metal cation with two background electrolyte factors: the pH and the concentration of a complexing agent. Imidazole, which has an electrophoretic mobility close to those of metal cations, was used as the visualization agent, and 2-hydroxyisobutyric acid (HIBA) was used as the complexing agent. Through computer modeling, the electrophoretic mobilities of fourteen metal cations were predicted on the basis of five initial experiments within the factor space of pH and HIBA concentration. Good agreement was observed between the predicted electrophoretic mobilities and the observed values of the metal cations. Subsequently, the separation of a complex mixture of metal cations was successfully optimized. A complete separation of 14 metal cations including alkali, alkaline earth and transition metal(II) cations was achieved within 4 min. In addition, the effectiveness of other visualization agents and complexing agents for the separation of metal cations was examined.