The Study Of Determination Of Trace Ions By Dual-indicator Catalytic-kinetic Spectrophotometry

In this paper, we reported several kinds of catalytic spectrophotometricmethods，which were determined by trace iron, nitrite or sulfur with dual-indicator. And westudied the experiment conditions，analyzed the linear relation between the reaction rateand concentration of catalytic. Therefore, we set up a new dual-indicator andcatalytic-spectrophotometric methods to test trace ions. We explored the factors thataffected the reaction rate, and discussed the catalytic mechanism of partial reaction system.The paper’s research contents mainly include:1. Trace iron was determined by dual-wavelength and dual-indicator catalyticspectrophotometric method, which was based on trace iron catalyzed oxidation of methylorange and crystal violet by hydrogen peroxide in the sulfuric acid solution. Theabsorbances of methyl orange and crystal violet systems at530nm and590nm weremeasured. The linear range of the determination was0.02-0.60μg/25mL, the detectionlimit for trace iron was3.46×10-5μg/25mL. We got a satisfied result in measurement oftrace iron in traditional Chinese medicine sample.2. We established a new catalytic reaction system in dual-indicator catalytic kineticsspectrophotometric method for the determination of trace amounts of NO－2. The systemwas in phosphate acid solution. It used NO－2catalyzing oxidation of methyl green-acidchrome blue by potassium bromated. The absorbance of methyl green-acid chrome bluesystems at540nm and635nm were measured. The linear range of the determination was0.20-2.80μg/25mL, the detection limit for NO－2was6.18×10-10g/mL. This method issimple and rapid, high sensitivity, stability, and has good selectivity. And it has animportant application value in water quality detection.3. We established a new method in dual-indicator catalytic kinetics spectrophotometricmethod for the determination of trace amounts of NO－2. The system was in phosphate acidsolution. It used NO－2catalyzing oxidation of acridine red-victoria blue.The absorbanceof acridine red-victoria blue systems at528nm and615nm were measured. The linearrange of the determination was0.20-2.80μg/25mL, the detection limit for NO－2was 2.54×10-10g/mL. We got a satisfied result in measurement of trace amounts of NO－2inwater quality detection.4. A new dual-wavelength and dual-indicator catalytic kinetics spectrophotometricmethod for determination of trace S2-was established in this paper. The method was basedon the sulfur ion suppression of catalytic reaction, which the iron was a catalyst inoxidation reaction of methyl orange and azure by hydrogen peroxide. The absorbance ofmethyl orange and azure systems at465nm and633nm were measured. The linear rangeof the determination was0.01-3.00μg/25mL, the detection limit for S2-was1.80×10-10g/mL. We got a satisfied in measurement of trace S2-in domestic water sample.All of these experimental results display that the catalytic-kinetic methods ofdual-indicator suffer from poor selectivity or sensitivity in spectrophotometric method.