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

Capillary electrophoresis for the determination of inorganic metal cat ions in the presence of Various complexing agents was investigated. Th e complexing agents studied were acetic, glycolic, lactic, hydroxyisob utyric, oxalic, malonic, malic, tartaric, succinic and citric acid. Th ey were ah suitable as complexing agents for separating a mixture of s ix alkali and alkaline earth metal ions (lithium, sodium, potassium, m agnesium, calcium and barium) using indirect W detection with imidazol e as a carrier buffer and background absorbance provider. The pH of th e carrier buffer affected the electrophoretic separation in a complex but predictable way. The optimum pH for separating these ions in the p resence 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 decrea se in the mobility of divalent ions and a decrease in number of theore tical plates, N, due to complex formation. In most of the cases report ed 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, an d N from 16000 to 750000 per metre. Of the ten complexing agents studi ed, lactic, succinic, hydroxyisobutyric and malonic acid seemed to giv e the best overall performance.