Phthalanilic acids as highly selective reagents for the amperometric determination of thorium(IV)

Th(IV) has been determined by amperometric titration at an applied emf of -1.0 V with ten phthalanilic acids. Of these, the 2,5-dichloro, 4-bromo, 3-nitro, 4-nitro and 1-naphthyl derivatives were found promising analytical reagents and most effective. Th(IV) in the range 11.6-1160 mg/10O ml can be determined with an error of +/- 0.3%. The possible interference of 46 ions was studied and only two. Pd(II) and Zr interfered; they could be masked by the addition of dimethylglyoxime or Nioxime, and pyrophosphate respectively.