The preconcentration with synergist-impregnated Polyurethane foams and spectrophotometric determination of trace thorium in natural waters

This paper reports the use of synergist-impregnated Polyurethane foams for preconcentrating trace thorium from natrual waters. The polyether type Polyurethane foams were employed, which were loaded with bis (2-ethylhexyl) phosphoric acid/tributyl phosphate/carbon tetrachloride (2:5:93, V/V/V) mixture. The surplus reagent was removed by filter paper. The loaded foams prepared in this way were dipped into the water sample and stirred for 20 minutes. The optimum conditions for preconcentration are: samples should be adjusted to about pH 1 and temperature kept within 30°-45°C. The distribution and phase ratios were calculated to be 4.26 x10⁴ and 2.01x10⁴ respectively, assuming that the mixture and water were totally immiscible with each other. The actural values were all slightly greater than the calculated ones. After removing the foam from the sample, the former was washed with water and subjected to wet oxidation with concentrated nitric and perchloric acids. The residue was taken up with dilute hydrochloric acid. The amount of thorium in the water sample was spectrophotometrically determined with Arsenazo III at 665 nm. The method is simple, rapid, accurate and inexpensive.