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Absolute values have been obtained by means of thermal ionisation mass spectrometry for the iron isotope abundance ratios of a sample of metallic iron of natural isotopic composition. This was achieved by calibrating the mass spectrometric measurement procedure using five different synthetic isotope mixtures, prepared from carefully characterised enriched isotope carrier compounds, 54Fe(2)O(3) and 56Fe(2)O(3). Three different mass spectrometric measurement procedures were developed, all using a silica-gel/boric acid ionisation enhancer. Measurements were carried out on two different instruments. The n(54Fe)/n(56Fe) ratio of the synthetic mixtures and of the natural iron isotopic reference material (IRM) were measured using a mass spectrometer with Faraday detector. Both the n(57 Fe)/n(56Fe) and n(58Fe)/n(56Fe) ratios of the natural iron IRM were determined using the same instrument but operated at a higher ionisation temperature (1430 C instead of 1350 C) and using an internal normalisation procedure. For the determination of the abundances of the minor isotopes in the enriched isotope carrier compounds, an instrument equipped with a calibrated ion counting device was used and the ionisation temperature was 1150 C. Using the latter instrument and method, the n(54Fe)/n(56Fe) ratio of the IRM was found to agree within 4 x 1.0 E-5 with the calibrated value of the Faraday measurements, indicating that experimental conditions were well controlled in both cases.

Additional information

Authors: TAYLOR P D P, JRC Geel (BE);DE BIEVRE P, JRC Geel (BE);MAECK R, Ciba-Geigy AG, Basel (CH)
Bibliographic Reference: Article: International Journal of Mass Spectrometry and Ion Processes, Vol. 121 (1992) pp. 111-125
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