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

Abstract

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. ^125mTe^IV was separated from an HCl solution in which ¹²⁵Sb and ^125mTe^IV were in radioactive equilibrium and ^125mTe was used as a tracer. The reactant (Te^IV) was oxidized sub-stoichiometrically with a solution of K₂Cr₂O₇ in 0.1 mol dm^–3 HCl, followed by the extraction of Te^IV with 20% tributyl phosphate–kerosene solution (after changing the concentration of HCl to 5 mol dm^–3) in order to separate Te^IV and Te^VI. Activities of Te^VI 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.