CAPILLARY ELECTROPHORETIC ANALYSIS OF INORGANIC CATIONS - ROLE OF COMPLEXING AGENT AND BUFFER PH

Capillary electrophoresis for the determination of inorganic metal cations in the presence of Various complexing agents was investigated. The complexing agents studied were acetic, glycolic, lactic, hydroxyisobutyric, oxalic, malonic, malic, tartaric, succinic and citric acid. They were ah suitable as complexing agents for separating a mixture of six alkali and alkaline earth metal ions (lithium, sodium, potassium, magnesium, calcium and barium) using indirect W detection with imidazole as a carrier buffer and background absorbance provider. The pH of the carrier buffer affected the electrophoretic separation in a complex but predictable way. The optimum pH for separating these ions in the presence of the complexing agent was around the pK(1) of the acid. When di- and triprotic acids were used, electrophoresis carried out above the second acid dissociation constant resulted in a significant decrease in the mobility of divalent ions and a decrease in number of theoretical plates, N, due to complex formation. In most of the cases reported here one could obtain, typically, a migration time span from 1 to 2 min, a minimum and a maximum resolution of 1 and 15, respectively, and N from 16000 to 750000 per metre. Of the ten complexing agents studied, lactic, succinic, hydroxyisobutyric and malonic acid seemed to give the best overall performance.