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[en] 2-(4-sulphophenylazo)-1,8-dihydroxynaphthalene-3,6-disulphonic acid (SPADNSA) forms complexes with Dy(III) and Ho(III) over the pH range 5.0-8.3. Two types of the complexes are formed: with a ratio of Me : SPADNSA=1 : 1 at pH values to 7.52 and with a ratio of 2 : 3 over the pH range 7.86-8.10. The stability of the complexes of Dy and Ho with SPADNSA is similar to that of the complexes of SPADNSA with La. A procedure has been developed of complexometric titration of rare earths with EDTA solution using SPADNSA as indicator. The procedure (visual and spectrophotometric) makes it possible to determine rapidly La, Pr, Nd, Sm, Cd, Th, Dy, and Ho over the concentration range 5X10 sup(-3)-5X10sup(-5) M with an error of less than 1.5%

[en] Thorium at concentrations down to 10^-₅M is determined by visual titration with N-(2-hydroxyethyl)ethylenediaminetriacetic acid at about pH 2.0 with SPADNS as indicator. The colour change is from violet to scarlet. The optimum range for the determination is 0.05-75mg/25ml. The relative standard deviation at the 50 μg/25ml level is 0.9%, and 0.3% for 1mg/25ml. The tolerance limits for various foreign ions have been established. The method finds use in the determination of thorium in monazite sand. (Author)

[en] The water fluoride levels in rivers and lakes, in a total of 26 different collection points placed within a circle of 10 km in diameter having the Nuclear Fuel Plant of Resende, Rio de Janeiro, as the center, were determined. (E.G.)

[en] Studies have been carried out potentiometrically on the complex formation of yttrium(III), zirconium(IV) and cerium(IV) with two azo dyes, Arsenazo I and Spadns. The enthalpies and entropies of complex formation and stability constants of the complexes have been determined. (K.B.)