Kunihiko Hasegawa

Determination of trace amounts of thallium in commercial radioactive 204Tl samples by the redox sub-superequivalence method of isotope dilution analysis

Trace amounts of thallium in a commercial radioactive 204Tl sample were determined using the sub-superequivalence method of isotope dilution analysis (SSE-IDA) and sub-stoicheiometric isotope dilution analysis (Subst-IDA), and the results obtained were compared. Before the determination, various conditions for oxidation and extraction were examined. An HCl-HClO4 mixture was the best solvent for oxidation by KBrO3 and 20% tributyl phosphate in benzene was suitable for the separation of TlIII. Under conditions where ordinary Subst-IDA gives large errors, accurate determinations with errors of a few per cent. were possible with SSE-IDA. The volume of the reaction solution was minimised in order to reduce the radioactive waste problem.

Determination of trace amounts of tellurium by the sub-superequivalence method of isotope dilution analysis

Trace amounts of tellurium in synthetic samples were determined by the redox sub-superequivalence method of isotope dilution analysis (SSE-IDA) and the results were compared with those of sub-stoichiometric isotope dilution analysis (Subst-IDA) in order to demonstrate the usefulness of SSE-IDA. 125mTeIV was separated from an HCl solution in which 125Sb and 125mTeIV were in radioactive equilibrium and 125mTe was used as a tracer. The reactant (TeIV) was oxidized sub-stoichiometrically with a solution of K2Cr2O7 in 0.1 mol dm–3 HCl, followed by the extraction of TeIV with 20% tributyl phosphate–kerosene solution (after changing the concentration of HCl to 5 mol dm–3) in order to separate TeIV and TeVI. Activities of TeVI in each aqueous phase were measured and the amount of tellurium was determined according to the graphical method of SSE or Subst-IDA. Under the conditions where Subst-IDA gives large errors, accurate determinations were possible using SSE-IDA with errors of less than 5–6 per cent. The limit of the determination was about 2 µg ml–1.