Spectrophotometric Determination of Gallium(III) with Rutin

Abstract

Gallium, naturally occuring in small concentrations on the order of 10 -100 µg g -1 in silicate rocks, 1 has found wide use in electronics and communication industries as GaAs and GaN, forming the basis of silicon-replaced integrated circuits and laser diodes. 2 GF-AAS, a sophisticated instrumental technique for trace gallium requiring well-trained operators, suffers from a lack of sensitivity, mainly ascribed to loss of vaporization of molecular Ga species during the heating process. 3 This type of interference could only be eliminated by the combined use of chemical modifiers with a tungsten-coated L'vov platform graphite tube. 4 For the spectrophotometric determination of gallium, Chromazurol S 5 and 4-(2-pyridylazo)resorcinol 6 have been used as chromogenic reagents in aqueous solution, and 2-(2-pyridylazo)-5-monoethyl-amino-p-cresol, 7 Rhodamine B,8,9 Np-chlorophenyl-2-furohydroxamic acid, 10 and 2-(2-(3,5-dibromopyridyl)azo)-5-diethylaminobenzoic acid 11 have been used in conjunction with solvent-extraction techniques. The instability of phenylfluorone and its Ga-chelate in ethanolic solution combined with the development of turbidity with time was overcome by the incorporation of a cationic surfactant (hexadecylpyridinium bromide) and pyridine. 12 The authors previously developed a carminic acid spectrophotometric determination of Ga where the colored chelate was solubilized in aqueous solution with hexadecylpyridinium chloride (HDPC) at pH 4.0. 13Agrawal and Bhatt concluded that the nonselectivity of the color reagent or a lack of suitable masking agents seriously limited the practical usefulness of most spectrophotometric procedures. 10 This work makes use of rutin, a flavonoid ligand containing carbonyl and four hydroxyl groups, in ammonium acetate solution at pH 7.0, where the chelate was solubilized with HDPB, and its absorbance recorded at 430 nm without requiring extraction with hazardous organic solvents. Rutin (C27H26O16H4) easily forms complexes with many metal cations, possibly through the 5-hydroxy-4-keto chelating site, 14 and with metal-containing anions, such as molybdate 15 and titanyl oxalate, 16 [TiO(C2O4)2] 2- (Fig. 1). Metals that can be spectrophotometrically determined with rutin include W 6+ , 17 Al, Ti and V, 18 Ni, 19 Zr, 20 and Mo 6+ . 21 In recent years, surfactants near critical micellar concentrations have found wide use in spectrophotometric metal analyses due to their favorable effects on the solubilization of metal chelates, on the shift of maximum absorption wavelength and an increase in the molar absorptivity of these chelates, and on changes in the ionization equilibria of the ligand. 22 ExperimentalAll spectral readings and recording were made using a Cary-1E UV-Vis spectrophotometer equipped with quartz cuvettes of 1 cm thickness; the pH measurements were made with a Metrohm Herisau E-512 pH-meter. With the exception of Ga 3+ and Pb 2+ nitrates (Fluka), all chemicals were purchased from E. Merck, and were of analytical reagent grade. Sphalerite (a (Zn, Fe)S mineral, al...

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