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

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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: Ba(2+)<Sr(2+)<Ca(2+)<Mg(2+) (Be(2+) 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, Ca(2+) and Mg(2+) in river, tap and underground water samples were determined; the detection limits of metal ions were about .10(-5)M (1M=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 Ca(2+) and Mg(2+) in a standard serum sample