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

Capillary electrophoresis of alkaline-earth metal ions was examined with a UV-absorbing chelating agent. The metal chelates separated in a capillary were measured by on-column UV-absorptive detection. When ethylenediaminetetraacetic 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 16 min using a capillary (50 mum i.d.) of 75-cm effective length (L(D)) at an applied voltage of 30 kV, and calcium and magnesium ions were separated within 4 min using a 25-cm capillary at an applied voltage of 20 kV. 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(-5) M (1 M=mol dm-3), and the relative standard deviations for the determination of around 10(-4) M 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.