Sequential separation and determination of thorium(IV) in calixarene hydroxamic acids

Abstract

A new calixarene hydroxamic acid, 25,26,27,28-tetrahydroxy5,11,17,23-tetrakis(N-p-chlorophenyl)calix[4]-arene hydroxamic acid (CPCHA) is used for the extraction and spectrophotometric determination of thorium(IV). The molar absorptivity of the thorium(IV)–CPCHA–SCN complex is 2.2 × 10⁴ m² mol^–1 at 450 nm. The system obeys Beer's law over the range 1.3–13.2 ppm of thorium. The thorium–calixarene hydroxamate ethyl acetate extract was directly subjected to ICP-AES measurements which increases the sensitivity by fifteen-fold. Thorium can be estimated at the 0.1 ppm level. The method is applied for the trace determination of thorium(IV) in geological samples at the low ppb level even after a 1 : 100 dilution (dissolution).