Clinical Chemistry, Vol 37, 2076-2080, Copyright © 1991 by American Association for Clinical Chemistry

31P nuclear magnetic resonance and zero-point titration compared for measuring free magnesium concentration in erythrocytes

WB Geven, GM Vogels-Mentink, JL Willems, CH von Os, CW Hilbers, JJ Joordens, G Rijksen and LA Monnens
Department of Pediatrics, University Hospital Nijmegen, University of Nijmegen, The Netherlands.

Intracellular ionized magnesium concentrations ([Mg2+]i) were measured in erythrocytes by 31P nuclear magnetic resonance (NMR) and zero-point titration in 14 controls and seven patients with renal magnesium loss. The mean intracellular ionized magnesium concentration in controls measured by 31P NMR was 0.20 (SD 0.03) mmol/L cell water, compared with 0.55 (SD 0.12) mmol/L cell water by zero-point titration. Total erythrocyte magnesium content measured with the lysate method was 0.63 mmol/L cell water higher than estimated by 31P NMR, probably because not all magnesium complexes are fully visible to the NMR technique. We found a positive correlation between plasma ultrafiltrable magnesium and [Mg2+]i irrespective of the [Mg2+]i assay used. [Mg2+]i measured with 31P NMR correlated modestly but significantly with [Mg2+]i determined by zero-point titration (r = 0.58, P less than 0.02). Washing erythrocytes before the zero-point titration decreased the ATP content and the cell water fraction, which led to overestimation of [Mg2+]i by zero-point titration. Although absolute values for [Mg2+]i differ with the assay used, both methods determined significantly lower values for [Mg2+]i in patients with isolated renal magnesium loss.

The following articles in journals at HighWire Press have cited this article:

				J. P. Willcocks, P. J. Mulquiney, J. C. Ellory, R. L. Veech, G. K. Radda, and K. Clarke Simultaneous Determination of Low Free Mg2+ and pH in Human Sickle Cells using 31P NMR Spectroscopy J. Biol. Chem., December 13, 2002; 277(51): 49911 - 49920. [Abstract] [Full Text] [PDF]