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

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.