Characterization procedure for ion-selective electrode assays of magnesium activity in aqueous solutions of physiological composition
Eugster, R.; Rusterholz, B.; Schmid, A.; Spichiger, U.E.; Simon, W.
Clinical Chemistry 39(5): 855-859
1993
ISSN/ISBN: 0009-9147 PMID: 8485876 Document Number: 420614
A magnesium ion-selective liquid membrane electrode based on a synthetic neutral carrier is presented. The selectivity for Mg-2+ over Na+, K+, and H+ is sufficient for assays in the physiological range, but a chemometric correction of apprx 10% is still necessary for the Ca-2+ interference. We optimized the membrane composition especially with respect to selectivity and accuracy by performing a new characterization procedure in which we simulated the variety of blood serum samples with 10 aqueous solutions. After a three-point calibration, these solutions were measured alternately with the middle-range calibrator for 3 min. The magnesium activity was evaluated after correcting for the calcium interference according to the Nikolsky equation. The selectivity coefficient, K-MgCa-pot, was itself fitted to give the minimum deviations from the assigned magnesium activities. Electrodes with an optimized membrane composition show an average deviation from the theoretical activity values of about 1.6% with logK-MgCa-pot = -0.8.