Study of the properties of rare-earth elements (REEs) and their alloys and compounds is important from the viewpoints of both practice and theory, because these elements, by virtue of their valuable properties, are widely used in state-of-the-art technologies. Rare-earth elements show considerable promise for metallurgy, machine building, instrument making, the glass industry, and medicine [1]. Rare-earth silicides and germanides are used in the reactor-building industry. The relative thermal stability of REE along with their large activation cross-sections for neutron capture allows them to be used as neutron-absorbing materials for different units. Rare-earth elements enter into the composition of scintillation materials as activators. The characteristics of these materials significantly depend on the concentrations of REEs; therefore, reliable, sensitive, selective, and rapid procedures are required for their quality control. Rare-earth elements are most often determined by atomic emission spectrometry, which allows impurities of individual lanthanides to be determined in the presence of others. Luminescence and spectrophotometry are also often used. These methods are sensitive and selective, but they often require unavailable and specific reagents. Voltammetric methods are competitive with the above methods and, at the same time, possess important advantages, such as the high sensitivity and reproducibility of the results, rapidity, the possibility of the simultaneous determination of several components, and the availability of equipment [2].The reduction of REE(III) ions, especially Eu(III) and Yb(III), has been studied quite well [3]. There is information on the effect of pH and the supporting electrolyte; the kinetics of the Eu(III) Eu(II) and Yb(III) Yb(II) conversions was studied in [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Eu(III) and Yb(III) can be determined at a dropping mercury electrode (d.m.e) in the presence of other REEs [11][12][13][19][20][21][22][23][24][25][26]. The studies of Eu(III) reduction in aqueous-organic and organic media showed that these media were unsuitable for determining europium(III) because of their low conductivities [27][28][29][30].The REE(III) ions are reduced in the potential range from -1.7 to -2.0 V. There is no unified opinion about the nature of their polarographic waves; different assumptions were made in [31-41]. These waves (or peaks) are obtained at the potentials close to the potentials of the supporting electrolyte reduction and, therefore, are poorly selective. REE(III) can be determined by the proposed procedures only after the electrochemical or chemical separation of foreign REE(III) and Al(III), Cd(II), Co(II), Cu(II), Ni(II), Pb(II), Zn(II), and other ions [33,[42][43][44][45][46]. Therefore, voltammetry in conventional supporting electrolytes offers no advantages over other methods and is rarely used.At present, more than 30 organic ligands have been proposed for the voltammetric determination of individual or combined REEs. The selectivit...

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Complexes of o , o '-substituted azo compounds are used for the voltammetric (VA) determination of Al(III) [1][2][3], Ga and In(III) [3], U(IV) [4], Zr(IV) [5,6], rareearth metals(III) [7][8][9][10][11], etc. In the majority of cases, an additional peak that corresponds to the reduction of a complex appears in the voltammograms. This allows several metals to be determined using the same reagent when complexes differing in stability are formed. It was shown that In(III) and rare-earth metals(III) could be simultaneously and rapidly determined by voltammetry using Eriochrome Red B (ERB) [12]. However, the electrode process of complex reduction has not been studied comprehensively. In this work, we studied the electrochemical behavior of the indium(III)-ERB complex by polarography with a linear sweep of the polarizing potential. EXPERIMENTALThe experiments were carried out using a digital voltammetric setup combined with a personal computer [13] and a three-electrode cell, whose temperature was maintained with a thermostat. A slowly dropping mercury electrode (DME), a saturated calomel electrode, and a platinum electrode served as the indicator, reference, and auxiliary electrodes, respectively. The characteristics of the capillary were as follows: m = 5.34 × 10 -4 g/s and τ c = 14.5 s in a 0.2 M NH 4 Cl solution with the circuit open. The dissolved oxygen was removed by purging purified argon. The pH of the solutions was controlled by an MV 870 DIGITAL-pH-MESS-GERÄT pH-meter. The required pH value was adjusted by HCl, NaOH, and acetate-ammonia buffer solutions. Spectrophotometric studies were carried out using a SPEKOL-11 instrument in cells with l = 1.0 cm. A 1 × 10 -2 M stock solution of indium(III) was prepared by dissolving a sample of the metal of 99.99% purity in the mixture of conc. HCl and HNO 3 of analytical grade [4]. A 1 × 10 -3 M ERB stock solution was prepared by dissolving the reagent in twice-distilled water and standardized according to [14]. RESULTS AND DISCUSSIONThe reduction of ERB at a DME was described in [10]. When a solution of indium(III) chloride was added to an ERB solution at pH 6.5-12.0, the yellow color of the solution changed to orange. An insignificant bathochromic shift of the adsorption band by 10-30 nm (depending on the pH of the solution) and a decrease in absorbance were observed in the electronic spectrum of the indium(III)-ERB complex with respect to the same parameters of the reagent spectrum. Such insignificant changes in the absorption spectra prevent the application of spectrophotometry to the studies of complexes.At pH 6.5-12.0, along with the reduction peaks of the dye ( P 1 and P 2 ), an additional cathodic peak ( P 3 ) appeared in the polarograms of ERB in the presence of indium(III) (Fig. 1). Indium(III) is not reduced under these conditions in the absence of ERB; therefore, peak P 3 corresponds to the reduction of the complex. Ammonia (pH 8.0-12.0), pyrophosphate (pH 8.0-12.0), and ARTICLES Abstract -The reduction of indium(III)-Eriochrome Red B complex is studied in...

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