Analytical procedures for the determination of uranium and thorium traces in aluminium

Different combined procedures involving element preconcentration and ICP-OES or polarography are described for the determination of the alpha emitters uranium and thorium in aluminium. The results are compared with those of instrumental neutron activation analysis. After extraction with ethyl acetate, uranium and thorium can be determined by ICP-OES (uranium detection limit, given as 3sub(SO), 12 ng/g, standard deviation 0.95 ng/g at 12.5 ng/g; thorium detection limit 8 ng/g, standard deviation 0.9ng/g at 12.5 ng/g). After a second extraction with tri-n-octyl phosphine oxide, uranium can be determined by polarography (detection limit 10 ng/g, standard deviation 4.4 ng/g at 200 ng/g). Thorium also can be coprecipitated with Fe(OH)3 and determined with ICP-OES (detection limit 5 ng/g, standard deviation 0.6 ng/g at 10 ng/g). The results obtained by wet chemical analyses lie within the spread of accuracy of the INAA results obtained by several laboratories. In general, the comparative results indicate that super pure aluminium containing less than 1 ng/g uranium and thorium can be produced. (Author)