SEQUENTIAL SEPARATION AND DETERMINATION OF THORIUM(IV) IN CALIXARENE HYDROXAMIC ACIDS

A new calixarene hydroxamic acid, ,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 absorptivit y of the thorium(IV)-CPCHA-SCN complex is 2.2 X 10(4) m(2) mol(-1) at 450 nm. The system obeys Beer's law over the range 1.3-13.2 ppm of tho rium. The thorium-calixarene hydroxamate ethyl acetate extract was dir ectly subjected to ICP-AES measurements which increases the sensitivit y 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 geolog ical samples at the low ppb level even after a 1:100 dilution (dissolu tion).