A method for the measurement of ionized magnesium

The role of ionized magnesium (Mg⁺⁺) in biological processes only recently has received experimental attention and is not yet clearly defined. Several efforts to develop ion-selective electrodes (ISEs) sensitive to magnesium have been reported, and significant progress has been achieved with the use of ionophore-based selective electrodes involving malondiamide subunits. We evaluated a magnesium ISE based on one of these carriers in the AVL 988-4 Na/Mg/Ca/pH analyzer (AVL Scientific, Roswell, Ga). We studied the performance of this analyzer in terms of precision, linearity, and relative accuracy. Precision of the electrode was excellent, with a linear response over the pathologically significant range. Accuracy of Mg⁺⁺ measurement is difficult to assess because of the lack of a reference method and primary standards. The ISE will provide the much-needed technology for evaluating the use of Mg⁺⁺ in patient care management.