A method for the detection and assay of iron stable isotope tracers in blood serum

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Abstract
Methodology for use of stable isotopes of iron (54Fe, 57Fe, and 58Fe) as biological tracers was developed. Tracers were quantitated by measurement of ion abundances with a quadrupole mass spectrometer. The volatility of the iron was enhanced by chelation with 2,4-pentanedione prior to analysis. Samples were introduced into the mass spectrometer via a direct inlet probe. Ion abundance ratios were calculated from integrated ion current measurements obtained for selected ions in the two-ligand fragment of the chelate. Stable isotope tracer concentrations were calculated from these ratios. A procedure was developed for the formation and purification of serum iron chelates. The method was used to analyze iron standards and blood serum samples containing known amounts of added 58Fe. The disappearance from pony serum of injected 58Fe was used as an in vivo test of the method. It was estimated that a minimum of 1.5 mg of either 54Fe, 57Fe, or 58Fe would be required to label 1 g of natural iron at detectable levels. The method has promise as an alternative to radioisotope tracer techniques for some applications involving human subjects.