EXTRACTION OF MAGNESIUM FROM BIOLOGICAL-FLUIDS USING 8-HYDROXYQUINOLINE AND CATION-EXCHANGE CHROMATOGRAPHY FOR ISOTOPIC ENRICHMENT ANALYSISUSING THERMAL IONIZATION MASS-SPECTROMETRY

The use of 8-hydroxyquinoline to precipitate magnesium was evaluated a s a method for preparing biological samples for isotopic enrichment an alysis using thermal ionization mass spectrometry (TIMS). Standard cur ves in matrices of water, serum, and urine were prepared using varying amounts of Mg-25. The Mg-25/Mg-24 isotope ratio was measured by TIMS using a silica gel/phosphoric acid technique. Although the total Mg re covered by precipitation from the matrices varied considerably and was dependent on matrix, recovery was sufficient for isotopic enrichment analysis. Urine samples required cation-exchange chromatography (Bio-R ex AG 50W-X8 filter membrane, Bio-Rad Laboratories) prior to precipita tion to remove contaminants which interfered with the thermal ionizati on process. The observed versus expected Mg-25/Mg-24 enrichments were evaluated using linear regression analysis: water, y = 0.016 + 1.022x; serum, y = 0.5 + 1.097x; urine, y = -0.004 + 0.943x. This method has proven useful for the isolation of magnesium from the biofluids tested .