Concurrent Calcium and Magnesium Determination by Ion Chromatography: An Approach to Avoid Interferences That Compromise Analysis

To evaluate phosphate-binding by calcium succinate and combinations of calcium and magnesium salts, ion chromatography (IC) methods were developed and validated for the determination of calcium and magnesium across the pH range in the human gastrointestinal tract (pH 1.2-6.8). Separation was achieved on a Dionex IC system using a Dionex IonPac CS12A column. Cations were eluted using 31 mM methanesulfonic acid and detected by suppressed conductivity. A method for calcium was validated according to USP Category 1 requirements and was applicable from 0.5 to 20 μg/mL calcium in 0.1 N HCl; 0.1 N acetate buffer, pH 4.5; or 0.1 N borate buffer, pH 6.8. A method for magnesium was validated independently and found applicable from 0.5 to 20 μg/mL magnesium in 0.1 N acetate buffer, pH 4.5 or 0.1 N borate buffer, pH 6.8. The validated method was successfully applied for the determination of phosphate-binding by calcium succinate and calcium acetate over the pH range found in the human gastrointestinal tract, and for monitoring the release of calcium succinate from encapsulated formulations. The validated method for calcium and magnesium was successfully used to determine phosphate-binding by combinations of calcium and magnesium salts in acetate or borate buffer solutions.