PRECONCENTRATION OF TRACE-ELEMENTS FROM HIGH-PURITY THORIUM AND URANIUM ON CHELEX-100 AND DETERMINATION BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY WITH ZEEMAN-EFFECT BACKGROUND CORRECTION

Preconcentration of trace impurities from large-sized samples of uranium metal and thorium oxide using a small column of Chelex-100 followed by their determination using graphite furnace atomic absorption spectrometry (GFAAS) is reported. A 0.5-10-g amount of the sample (uranium metal or thorium oxide) was dissolved, complexed with ammonium carbonate and subjected to the ion-exchange procedure. The retained analytes were eluted with 2-4 M nitric acid and brought to a small volume for a final dilution to 10-25 mi for their determination using GFAAS. The validity of the separation procedure and recoveries at mu g kg(-1) levels was checked by standard addition; the recoveries were > 95%.