A microassay for serum dialyzable calcium and magnesium by ion chromatography

We describe a method for determining dialyzable calcium and dialyzable magnesium in 50-microliter volumes of routinely handled aerobic serum. Calcium and magnesium concentrations were measured by ion chromatography after a 1-min equilibrium dialysis. Day-to-day precision (coefficient of variation, CV) was 3.8% for dialyzable calcium and 4.5% for dialyzable magnesium. Dilution of serum with water 1:1 as well as storage at 4 or -20 degrees C had no significant effects. Reference intervals for dialyzable calcium (58.1-68.1 mg/l) and magnesium (12.3-17.1 mg/l) were determined for 26 healthy adults. Lack of interference and the ability to determine simultaneously several analytes on a single specimen are advantages of the chromatographic method.