MEASUREMENT OF SULFATE CONCENTRATIONS AND TRACER TRACEE RATIOS IN BIOLOGICAL-FLUIDS BY ELECTROSPRAY TANDEM MASS-SPECTROMETRY/

A reproducible and very sensitive method is described for the quantita tion of inorganic sulfate in biological fluids by negative electrospra y ionization tandem mass spectrometry. After addition to the sample of S-34-labeled sodium sulfate internal standard and deproteinization wi th methanol, interfering bicarbonate anions are removed by acidificati on and chloride and phosphate by means of a single filtration step. Th e tandem mass spectrometer is used in neutral loss mode to detect HSO4 - ions free of interference from residual isobaric H2PO4- ions. Organi c sulfates do not interfere with the measurement. Serum and urinary in organic sulfate concentrations measured with this technique agree clos ely with determinations by ion-exchange chromatography with conductivi ty detection. Unlike the latter method, this technique does not requir e dedicated equipment. The method is also suitable for measuring the r atio of S-34-labeled sulfate to unlabeled sulfate in serum and hence r epresents an attractive alternative for the use of the radioactive S-3 5 isotope in human studies of body composition and oxidation of sulfur -containing substrates to sulfate. (C) 1998 Academic Press.