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  • 1 Slovak Technical University Department of Environmental Science Bratislava Czechoslovakia
  • | 2 Water Research Institute Bratislava Czechoslovakia
  • | 3 Slovak Technical University Central Laboratory of Chemical Techniques Bratislava Czechoslovakia
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Trace amounts of thyroxine in model samples (160.0–1 and 20.0–1), and thyroxine and 3,5,3-triiodothyronine in blood plasma were determined by sub- superequivalence isotope dilution analysis and radio-immunoassay technique. Hormones were labelled by125I. The separation of antibody-bound hormone from free hormone was performed by ultracentrifugation. The results show higher accuracy of the sub- super-equivalence isotope dilution method over that of radioimunoassay.