Abstract: The Interlaboratory Study for Fe Using Isotope Dilution Mass Spectrometry (IDMS)as the Reference MethodZhao Motian; Wang Jun(National Research Centre for Certified Reference Materials, Beijing 10013, China)Abstract: In this paper the method for determining Fe in the CIPM solution Ⅱ is described for the first interlaboratory study of the CIMP Working Group on Metrology in Chemical Analysis. The concentration of enriched isotope solution of 57Fe was certified with the standard solution of Fe as spike by IDMS. Then the content of Fe in the CIPM solution Ⅱ was determined with certified enriched isotopic solution as spike. The measurement result shows that the content of Fe in the CIPM solution Ⅱ is 32.10±0.11(μg.g-1). This result as compared with other interlaboratiory values is the best.Keywords: isotope dilution mass spectrometry; international coordinate study; iron