Migration behaviour of alkali and alkaline-earth metal ion-EDTA complexes and quantitative analysis of magnesium in real samples by capillary electrophoresis with indirect ultraviolet detection

Abstract

A capillary electrophoretic (CE) method was developed for the separation of some common alkali and alkaline-earth metal ions using EDTA as complexing agent and pyridine as UV chromophore for indirect detection at pH 5.00. Effects of pH and concentration of complexing agent on the differences in the effective mobilities between two ions were considered and equations derived were used to deduce the optimum conditions for their separation. Baseline separation of a group of metal ions, including K, Na, Li, Mg, Sr and Ba, was achieved in less than 4 min. The calibration range for magnesium was found to be linear up to 1.00 μg/ml when samples were prepared in the running buffer while a hyperbolic calibration curve was obtained when prepared in water. Application of the method to the analysis of magnesium in river water, urine and a solid sample of calcium carbonate was demonstrated. Magnesium in those samples was determined to be 812 μg/ml, 78.0 μg/ml and 0.023% (w/w), respectively, with reproducibilities between 5-9% R.S.D. in terms of peak height depending on sample matrices.