| Iron is considered as an essential micronutrient for animals, plants and human beings. And this element is also considered as an ambient contaminant in the environment. Some conventional determination methods of iron (Ⅲ) can be applied only after preliminary treatment and pre-concentration; the operation is more tedious and they need expensive instruments and reagents. In recent years, the analysis method based on catalyzed kinetic reaction has been developed and been proved to be an attractive means for trace analysis.In this paper a new analysis method is established for determination of trace iron (Ⅲ) based on the catalytic kinetic theory. The mechanistic of the reaction is studied, the iron in fresh water and sea water are determined with the new method. The main results of the research are as follows:1. A new catalytic kinetic spectrophotometric method is established for thedetermination of trace iron (Ⅲ).A new kinetic spectrophotometric method has been developed for the determination of iron (Ⅲ). The method is based on the catalytic effect of iron (Ⅲ) on the oxidation of weak acid brilliant blue dye (RAWL) by KIO4 in acid medium. The results from the orthogonal experiments and the single experiments show that the optimal experimental conditions are as following: 40mg/L RAWL, pH 3.15, 1.2×10-4mol/L Potassium periodate solution, reaction time 7minutes,8.0×10-4 mol/L phenanthroline, reaction temperature 25℃. Under the optimum conditions, the proposed method allows the determination of iron (Ⅲ)in the range 020. 0ng/mL and the detection limit is down to 4.10×10-10g/mL. The recovery efficiency in determining the standard iron (Ⅲ) solution is in the range of 98.0% - 100.5% and the RSD is the range of 1.9% - 3.1% .Moreover, it is found that most cations and anions do not interfere with the determination of iron (Ⅲ). Compared with other kinetic catalytic methods and instrumental methods, it is found that the proposed method shows fairly good selectivity and sensitivity, simplicity, cheapness, low detection limit and rapidity. It can be operated on the boat easily.2. In the paper the kinetic parameters of the reaction are studied and the mechanism of the reaction is investigated.The reaction orders with respect to each reagent are determined and are found to be 1/2,1/2,1/1 and 0 for potassium periodate, RAWL, iron (Ⅲ) and phenanthroline, respectively. On the basis of these values the kinetic equation of the reaction may bewritten as:-dCk/dt=kCK1/2CR1/2C(Fe3+1/2Cp0 The mean value of the apparentactivation energy of the reaction is found to be -19. 72 kJ/mol, and the apparent reaction rate constant is 0.0560 min-1.3. The new method has been successfully applied for the determination of iron (Ⅲ) in fresh water samples.The iron (Ⅲ) in the tap water and mineral water has been detemined respectively with the new method. The RSD of the method is the range of 0.33% - 1.68%, and the recovery rate of the method is in the range of 96.1% - 103.0%. The results are compared to those obtained by the AAS method. Good agreement is achieved. It proves that the new method can be successfully applied for the determination of iron (Ⅲ) in fresh water samples.4. The new method has been successfully applied for the determination of iron (Ⅲ) in seawater samplesThe iron(Ⅲ) in the seawater of the Jiaozhou Bay have been detemined respectively with the new method. The RSD of the method is the range of 0.33%-1.86% and the recovery rate of the method is in the range of 96.9%- 103.3%. The results are compared to those obtained by the AAS method. Good agreement is achieved. It proves that the new method can be successfully applied for the determination of iron(Ⅲ) in different seawater samples. |
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