MEASUREMENT OF IRON ISOTOPES (FE-54, FE-56, FE-57, AND FE-58) IN SUBMICROGRAM QUANTITIES OF IRON

Iron isotopes offer an excellent opportunity for detailed tracing of natural processes because of the range of stable isotopes (54, 56, 57, 58) and the importance of iron redox transitions in biochemical and inorganic processes. In this paper, we describe a significantly improved mass spectrometric technique for iron isotopic analysis that utilizes ion pulse counting detection and is calibrated with an absolute iron isotope abundance standard. All four stable iron isotopes are quantified in a single analysis to approximately 0.1% precision and accuracy using a low-temperature (1200-degrees-C) silica gel/boric acid technique on an improved source filament assembly composed of platinum and ceramic. Filament loads of 100-1000 ng can be utilized through implementation of an ultraclean work environment, improved chemistry, and a source designed specifically to minimize isobaric interference in the mass 50-60 region.