EDTAを用いる微量コバルトイオンの放射滴定

概要

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The radiometric titration of trace amounts of cobalt with EDTA has been investigated. After known amounts of EDTA are added to a series of aliquots of the sample solution containing 60Co, the free metal ion is separated from the EDTA complex by the chelating resin or cation-exchange resin. The radioactivity of the supernatant solution that contains the complex is measured to determine the end point of the titration. The optimum pH and the lowest determinable concentration of this trace analysis are discussed. The experimental results show that 10-6 or 10-7M of cobalt can be determined. The titration of both ferric and cobaltous ions in the mixture is possible. The mixture of cobaltous and zinc ions is analysed by a replacement titration. After adding EDTA equivalent to the total amount of the both ions and 65Zn as an indicator, the Co(II)-EDTA complex is oxidized to the Co(III) complex. Finally Zn-EDTA complex is titrated with the Fe(III) standard solution. Zinc in the EDTA complex is replaced by ferric ion and separated from the cobalt(III) and iron(III) complexes using a cation-exchange resin. The end point of the titration is determined from the radioactivity of 65Zn in the supernatant solution.
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