Separation and Determination of Alkaline-Earth Metal Ions as UV- Absorbing Chelates with EDTA by Capillary Electrophoresis. Determination of Calcium and Magnesium in Water and Serum Samples

Abstract

Capillary electrophoresis of alkaline-earth metal ions was examined with a UV-absorbing chelating agent. The metal1 chelates separated in a capillary were measured by on-column UV-absorptive detection. When ethylenediamine-tetraacetic acid (EDTA) was used as an chelating agent in a carrier solution (pH 9.2), the order of the migration time (t_m) of metal ions was as follows: Ba²⁺<Sr²⁺<Ca²⁺<Mg²⁺ (Be²⁺ could not be detected). These four ions were separated within 16min using a capillary (50μm i.d.) of 75-cm effective length (L_D) at an applied voltage of 30kV, and calcium and magnesium ions were separated within 4min using a 25-cm capillary at an applied voltage of 20kV. By using a 50-cm or 25-cm capillary, Ca²⁺ and Mg²⁺ in river, tap and underground water samples were determined; the detection limits of metal ions were about .10^-5M (1M=mol dm^-3), and the relative standard deviations for the determination of around 10^-4M of the metal ions were less than 2.0%. The method was also applied to the determination of Ca²⁺ and Mg²⁺ in a standard serum sample.