Spectrophotometric determination of molybdenic acid and zirconium(IV) with phenylfluorone and cetylpyridinium chloride

Abstract

In the presence of excess cetylpyridinium chloride (CPC) in an acidic solution molybdenic acid(MoO42-) forms a water soluble complex with phenylfluorone, whose color was very stable. The color development of a water soluble reddish brown complex between phenylfluorone and Zr(IV) enhanced by the catalytic action of sodium fluoride, particluary in the coexistence of excess CPC which increased the absorbance of the complex. Their absorption maximum wavelength were at about 540 nm (MoO42-), 560 nm {Zr(IV)} against the reagent blank, and the coloration was stable over the pH range from 1.2 to 1.9 (pH was adjusted with NaCl glycocohol-HCl buffer solution) and pH range from 4.2 to 5.2 (pH was adjusted CH3COONa-CH3COOH buffer solution). A linear calibration curve was obtained for 460 μg MoO42-/10 ml and 07 μg Zr(IV)/10 ml. According to Sandell's expression the sensitivities were 0.01 μg/cm2 of MoO42- and 0.002 μg/cm2 of Zr(IV) for absorbance of 0.001. From the data, the recommended analytical procedures of MoO42-, and Zr(IV) are as follows.A sample containing 460 μg MoO42- is taken in a 10.0 ml measuring flask, and 1.0 ml of 1.0 × 10-2 M CPC solution, 2.0 ml of buffer solution(pH 1.5), and 2.0 ml of 1.0 × 10-3 M phenylfluorone methanolic solution are added. The solution is diluted to 10.0 ml with water, and allowed to stand at 45°C for 30 minutes, the absorbance of phenylfluorone-MoO42--CPC complex is measured at 540 nm against the reagent blank. To the solution of Zr(IV) is added each 1.5 ml of 1.0 × 10-2 M CPC solution, 0.8 ml of 1.0 × 10-2 M sodium fluoride solution, 1.0 ml of 2.0 × 10-3 M methanolic phenylfluorone solution, and 1.5 ml of buffer solution (pH 4.6). After making up to the volume to 10.0 ml and allowing it to stand for 10 minutes, the absorbance is measured at 560 nm against the reagent. The effects of diverse ions on the absorbance of the complex were examined and shown.