|Budget Amount *help
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 2002: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2001: ¥2,000,000 (Direct Cost: ¥2,000,000)
The study of natural isotopic variations for heavier elements (e. g. , Fe, Cu, Zn or Ge) had a significant influence in many research fields such as biology, planetary, Earth, and environmental sciences. Recent series of isotopic study for transition metals revealed that the isotopic compositions of Fe and Zn were largely fractionated through biologically induced processes. This indicates that isotopic ratios of heavy elements can be used as a new biomarker for geological samples (Isotopic Biomarker). However, the mechanisms of large isotopic fractionation of heavy elements were still unclear. In order to understand the mechanism of large isotopic fractionation of heavy elements, and also to discuss the genetic link between the large isotopic fractionation and biological processes, further precise and reliable isotopic data must be obtained from series of biochemical samples.
Detection of natural variation in isotopic composition of the heavy elements was very difficult because of their
small magnitude of isotopic fractionation mainly due to small relative mass differences. To overcome this, sensitive and precise isotopic ratio measurements for heavy elements, especially for transition metals, have been made by means of a multiplecollector-ICP-Mass Spectrometry (MC-ICPMS). The precision and repeatability of the isotopic ratio measurements can be remarkably improved by a combination of sample-standard bracketing technique and newly developed correction for slow response of the Faraday preamplifiers. The precision and reliability of the resulted Fe and Zn isotopic ratio data were comparable to the isotopic data obtained by a thermal ionisation-mass spectrometry (TIMS). It should be noted that total amount of Zn and Fe required for the ICPMS measurements were almost order of magnitude lower than those for TIMS technique. This indicates that the ICPMS technique becomes now standard technique for sensitive and rapid isotopic ratio measurements for most transition metals.
The isotopic ratios of Fe and Zn in human blood cell (BRC) samples were measured. No significant seasonal change could be found both for Fe and Zn obtained from series of 12-month RBC samples. This can be explained by a small exchange efficiency (1 mg per day) of these elements in human body. The Fe isotopes in the RBC samples were largely fractionated (~1.5‰/amu), whereas Zn isotopes in the RBC samples showed very small variations (~0.3‰/amu). Moreover, lighter-Fe isotopes were enriched in the RBC samples, whilst heavier-Zn isotopes were enriched in the RBC samples. This indicates the clear difference in intake or metabolic efficiencies of these elements. Another interesting feature observed on Fe and Zn isotopes in the RBC samples were that isotopic ratios of Fe for male human bodies were significantly lighter than Fe isotopic composition of female bodies. This indicates that intake efficiency of Fe for male bodies were less effective than that for female bodies. The data presented here demonstrate clearly that the Fe and Zn isotopic ratios obtained by the ICPMS technique can give strong clues to elucidate the isotopic fractionation of transition metals occurring in biochemical reactions. Less