| The catalytic-spectrophotometric methods for the determination of trace iron or manganese with dual-indicator were discussed. The methods are based on the catalytic effect of ions 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. An elementary mechanism is proposed in the research to investigate the catalysis process and the results have certain theory and application value. The main work of this paper will lay a foundation for the establishment of new kinetic methods and the simultaneous determination of ions.The problems that were solved were as follows: (1)The selection of indicator; (2) The simultaneous determinations of multi-components; (3) the mechanism of catalytic reaction. The paper's research contents mainly include:1,A catalytic spectrophotometric method for the determination of iron(III) was established. Iron(III) was determined by dual-indicator catalytic spectrophotometric method which was based on the iron (III) catalyzing oxidation of alizarin red and rhodamine B by hydrogen peroxide in the sulfuric acid medium. The absorbances of catalytic and uncatalytic systems at 430 nm and 560 nm were measured.A new catalytic spectrophotometric method for the determination of trace iron was established. The linear range of the determination was 0.02～0.2μg /mL and 0. 2～0.32μg/mL, the detection limit for iron was 5.04×10-11 g/mL. The method has high sensitivity, good selectivity and stability. The operation of the system is simple and its reagents is easy to get. The method has been applied to determination of trace iron(Ⅲ) in tea sample with satisfactory results. 2,A new method dual-indicator catalytic kinetics spectrophotometric method for the determination of trace amounts of manganese was established. Manfanese was determined by dual-wavelength and dual-indicator catalytic spectrophotometric method which was based on the manganese catalyzed oxidation of light green and the dimethyl yellow by potassium periodate in the acetic acid and sodium acetate medium. The obsorbance of the catalytic and uncatalytic systems were measured at 430nm and 600nm.Under the optimum conditions, the linear range of this method is 0.15 2.2μg/25mL and the detection was 1.24×10-4μg/25mL This method has high sensitivity, system stable, a better selectivity. The determination of Manganese was applied to determine the manganese in flour and rice and the results was satisfactory.3,The new catalytic kinetics spectrophotometric method for determination of trace iron was proposed in this paper. The method was based on the fading indication reaction, which use iron as catalyst, between methylene blue and rhodamine B using hydrogen peroxide as oxidant in acetic acid and sodium acetate medium. The best experimental conditions and kinetic parameters were studied through experiments. The determination of iron by dual-wavelenth dual-indicator catalytic kinetics spectrophotometry through measuring the changes of catalytic and uncatalytic systems at 560 nm and 670nm. The linear range of the method was 0.2～2.8μg /25mL and the detection limitation was 6.64×10-11 g/mL L. This method has high sensitivity, stablity, good selectivity. The determination of iron was applied to practical sample with satisfactory results.4,A dual-wavelength dual-indicator catalytic kinetic spectrophotometric method for the determination of trace iron in sulfuric acid medium was studied. It was based on the catalytic effect of iron on the oxidation of methyl orange and light green by hydrogen peroxide. The absorbance of catalytic system and noncatalytic system were measured at 510 nm and 640 nm. Under the optimum conditions, the linear range of the determination of trace vanadium was 8 200μg / L. The detection limit was 1.12×10-10g/L and the relative standard deviation (n = 12) was 0.067 % for 20.0μg/L iron. This method has high sensitivity, stability and good selectivity. The method was applied to tea sample with satisfactory results. 5,A new catalytic kinetics spectrophotometric method for determination of trace iron(Ⅲ) was proposed in this paper. It was based on remarkable catalytic effect of iron(Ⅲ) on the oxidation of methylene blue by hydrogen peroxide in hydrochloric acid medium. The best experimental conditions and the reaction mechanism were studied through experiments. The maximum absorption peaks were 610 nm and 666nm. The linear range of the method was 0. 2～3.0μg/25mL and the detection limitation was 9.24×10-11 g/mL. This method has high sensitivity, stablity, good selectivity. The operation of the system is simple. The method has been applied to determination of trace iron(Ⅲ) in tea 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 developed the. application scope of kinetics analysis.
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