Thorium(IV) was quantitatively extracted at pH 7.5 with 0.0001M of hexaacetato calix(6)arene in toluene and after stripping
with 0.05M nitric acid, it was determined spectrophotometrically at 545 nm with thoron. Thorium(IV) was separated from commonly
associated elements in fission products like uranium(VI), cesium(I), lead(II), strontium(II) and cerium(IV) in varying proportions.
The method is simple, rapid, selective and applicable for the microgram concentrations of thorium(IV).