| Abstract: The catalytic-spectrophotometric methods for the determination of trace chromium or copper with dual-indicator were studied. The methods are based on the catalytic effect of chromium or copper on the oxidation of indicators. In the dual-indicator reaction system, the reaction rate was proportional to concentration of catalysts and the determination sensitivity was better than single-indicator system. The dependence of the indicator reaction rate on the reaction variables including the amounts of reagent, reaction solvent,,reaction time and reaction temperature have been studied. According to these,working curve was designed. The paper's research contents mainly include:1,A catalytic spectrophotometric method for the determination of trace copper was established. Copper was determined by dual-indicator catalytic spectrophotometric method which was based on the catalytic effect of copper on the oxidation of bromocresol purple and neutral red by hydrogen peroxide in NH3-NH4Cl medium at pH 9.65. The absorbance of catalytic system and uncatalytic system were measured at 460 nm and 590 nm. Under the optimum conditions, the linear range of the determination of trace copper was 0.00600.072μg/mL. The detection limit was 8.0×10-12 g/mL. The relative standard deviation was 2.9% ( n = 11). The method was applied to the determination of trace copper in flour and rice with satisfactory results.2,A catalytic spectrophotometric method for the determination of trace chromium(Ⅵ) was studied.Chromium was determined by dual-indicator catalytic spectrophotometric method which was based on the chromium(Ⅵ) catalyzed oxidation of rhodamine B and phenol red by hydrogen peroxide in the HAc-NaAc buffer solution. The absorbance of the catalytic and uncatalytic systems were measured at 430nm and 550nm.The linear range of determination was 0.010～3.30μg/25ml. The detection limit was 3.2×10-10 g/ml.The method is simple and of high sensitivity and good selectivity. It was applied to the determination of chromium in water.3,A new dual-wavelength dual-indicator catalytic kinetic spetrophotometric method for the determination of trace chromium was proposed. It was based on the catalytic effect of chromium(Ⅵ) on the oxidation of methylene blue and rhodamine B by hydrogen peroxide in HAc-NaAc buffer medium at pH 4.8. The absorbance of catalytic system and uncatalytic system were measured at 555 nm and 665 nm. Under the optimum conditions, the linear range of the determination of trace chromium(Ⅵ) was 0.0251.40μg/25mL. The detection limit was 5.2×10-10 g/mL. The method is simple, high sensitivity and good selectivity. The method was applied to the determination of trace chromium(Ⅵ) in waste water with satisfactory results.4,This paper establishes a dual-wavelength dual-indicator catalytic kinetic spectrophotometric method for the determination of trace of chromium(VI) on the oxidation of Leather green sf and Phenolsulfonphthalein by hydrogen peroxide in the media HAc-NaAc buffer medium. The absorbance of catalytic system and uncatalytic system were measured at 432nm and 640nm. Under the optimum conditions, , the linear range of the determination of trace chromium(VI) was 0.0080.360 g/ml,the correlation coefficient was 0.99359. The detection limit was 0.26278 g/L.The method is simple, stability, high sensitivity and better selectibity for the sample of trace chromium(VI) determination ideal .5,A dual-wavelength dual-indicator catalytic kinetic spetrophotometric method for the determination of trace chromium(VI) was studied . It was based on the catalytic effect of chromium(VI) on the oxidation of phenol red and methylene blue by hydrogen peroxide in HAc-NaAc buffer medium at pH 4.9 . The absorbance of catalytic system and uncatalytic system were measured at 434 nm and 670 nm . Under the optimum conditions , the linear range of the determination of trace chromium(VI) was 0.008～0.112mg/L . The detection limit was 2.02E-10 g/mL . The method is simple , high sensitivity and good selectivity . The method was applied to the determination of trace chromium(VI) in sample with satisfactory results .The experimental results indicate that the catalytic-kinetic methods of single-indicator suffer from poor selectivity or sensitivity towards some ions. The reaction of dual-indicator system is a new catalytic-kinetic method which could overcome these disadvantages. It also could simplify the process of the simultaneous determination of catalysts and develop the. application scope of kinetics analysis.
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