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 n atural processes because of the range of stable isotopes (54, 56, 57, 58) and the importance of iron redox transitions in biochemical and in organic 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 quantifi ed in a single analysis to approximately 0.1% precision and accuracy u sing a low-temperature (1200-degrees-C) silica gel/boric acid techniqu e on an improved source filament assembly composed of platinum and cer amic. Filament loads of 100-1000 ng can be utilized through implementa tion of an ultraclean work environment, improved chemistry, and a sour ce designed specifically to minimize isobaric interference in the mass 50-60 region.