Extractive—spectrophotometric determination of americium at trace levels with arsenazo-III

Americium(III) can be quantitatively extracted with 1 M diisoamylsulphoxide in Solvesso-100 from aqueous 0.02 M HNO₃—2.5 Al(NO₃)₃ solutions and, after dilution of the extract with ethanol and nitric acid, determined in the organic phase with arsenazo-III. The apparent molar absorptivity is 1.58 × 10⁵ l mol^-1 cm^-1 at 652 nm. The system obeys Beer's law within the range 0.1–1.6 μg Am ml^-1; 0.11 μg Am ml^-1 is determined with a reproducibility better than ±2%. Relatively large amounts of Ca(II), Cr(III), Fe (III), U(VI), Cl^-, NO₂^-, NO₃^- and F^- are tolerated. Interferences of Ce(IV), Pu(IV) and Th(IV) are eliminated by prior extraction with 2-thenoyltrifluoroacetone; only europium(III) interferes appreciably. Colour development is almost instantaneous and absorbances are virtually constant for 12 h.