Study And Application Of Determination Of Trace Vanadium(Ⅴ) And Vanadium(Ⅳ) In Water By The Catalytic Kinetic Spectrophotometric Method

Vanadium is considered as an essential micronutrient element. It is very meaningful to know about the content and distribution of vanadium(Ⅴ) and vanadium(Ⅳ) in wa-ter for chemical oceanography , environmental science and biogeochemistry research. At present, the determination methods of vanadium in water can be used only after pre-liminary treatment and preconcentration.The operations are very tedious and the analy-sis cost is high. The catalytic dynamic analytic method has higher sensitivity and speci-ficity and is widely applied in trace analysis as a powerful method.In this paper, new analytic methods are respectively established for the determination of trace amount vanadium(Ⅴ) and vanadium(Ⅳ) based on the catalytic kinetic theory. Besides the kinetic parameters of the reactions of vanadium(Ⅴ) and vanadium(Ⅳ) are separately discussed.Through research, the new methods are used for the immediate determination of trace amount of vanadium(Ⅴ) and vanadium(Ⅳ) in water. The new established methods can successfully determine the concentration of vanadium(Ⅴ) and vanadium(Ⅳ) in fresh water as well as vanadium(Ⅴ) in sea water with satisfying results. The main achievements of the research are as follows:1. A new catalytic kinetic spectrophotometric method is successfully established for the determination of trace vanadium(Ⅴ) at room temperature. The proposed method owns fairly good selectivity and sensitivity, simplicity, cheapness, low detection limit and rapidity.①A new reaction system is put forward for the determination of trace vanadium(Ⅴ) using RAWL as indicator, potassium bromate as oxidant and citric acid as activa-tion reagent.②The results from the orthogonal experiments and the single factor experiments of vanadium(Ⅴ) show that the optimal experimental conditions are as following: 1×10-4mol/L RAWL, 3.00×10-2mol/L KBrO3, 9.00×10-3 mol/L citric acid, pH = 2.50, the testing time is 7.0 min and the testing temperature is 25.0℃.③Under the optimum condition, the proposed method allows the determination of vanadium(Ⅴ) in the range 0～70.0 ng/mL, the detection limit is 0.407 ng/mL.The recovery efficiency in determining the standard vanadium(Ⅴ) solution is in the range of 98.5%～102%, and the RSD is in the range of 0.76%～1.25% .Moreover, it's found that most cations and anions do not interfere with the determination of vanadium(Ⅴ) under the analytical condition.④The kinetic parameters of the reaction are studied.The reaction orders with respect to each reagent are determined and found to be 1, 1/2, 1 and 1/2 for RAWL, potas-sium bromate, vanadium(Ⅴ) and citric acid. The mean value of the apparent activa-tion energy of the reaction is found to be 36.20 kJ.mol-1, and the apparent reaction rate constant is 0.0334 min-1. On the basis of these values the kinetic equation of vanadium(Ⅴ) can be written as: ddctR KcRc1K /2cV5 c1N/2⑤The new method is successfully applied for the determination of vanadium(Ⅴ) in fresh water samples.The vanadium(Ⅴ) in the tap water, and the Yellow River are detemined respectively with the new method. The RSD is in the range of 0.54%～1.43%, and the recovery rate is in the range of 98.3%～103.2%. It proves that the new method can be successfully applied for the determination of vanadium(Ⅴ) in fresh water samples with satisfactory results .⑥The new method is also successfully applied for the determination of vanadium(Ⅴ) in seawater samples.The RSD of the method is in the range of 0.51%～2.05% and the recovery rate of the method is in the range of 95.9%～104.2%.It proves that the new method can be successfully applied for the determination of vanadium(Ⅴ) in seawater samples.⑦Vanadium(Ⅴ) in the sea water of Qingdao offshore is determined using the method and the relative distribution map of vanadium(Ⅴ) is drawn up.2. On the other hand,a new catalytic kinetic spectrophotometric method is successfully established for the determination of vanadium(Ⅳ),too ①A new reaction system is esteblished for the determination of trace vanadium(Ⅳ) using RAWL as indicator, potassium bromate as oxidant and citric acid as activa-tion reagent.The proposed method has fairly good selectivity and sensitivity, sim-plicity, cheapness, low detection limit and rapidity.②The results from the orthogonal experiments and the single factor experiments of vanadium(Ⅳ) show that the optimal experimental conditions are as following: 7×10-5mol/L RAWL, 8.00×10-3mol/L KBrO3, 1.20×10-2 mol/L citric acid, pH=1.50, the reaction time is 5.0 min and the temperature is 35.0℃.③Under the optimum condition, the proposed method allows the determination of vanadium(Ⅳ) in the range 0～40.0ng/mL, the detection limit is 0.461ng/mL.The recovery efficiency in determining the standard vanadium(Ⅳ) solution is in the range of 97%～101.5%, and the RSD is in the range of 0.87%～1.60% .Moreover, it's found that most cations and anions do not interfere with the determination of vanadium(Ⅳ).④In the paper, the kinetic parameters of the reaction are studied .The reaction orders of each reagent are determined and found to be 1, 1, 1 and 1/2 for RAWL, potas-sium bromate, vanadium(Ⅳ) and citric acid. The mean value of the apparent activa-tion energy of the reaction is found to be 49.06 kJ.mol-1, and the apparent reaction rate constant is 0.0114min-1.On the basis of these values the kinetic equation of va-nadium(Ⅳ) can be written as: ddctR KcRcKcV4 c1N/2⑤The new method has been successfully applied for the determination of vana-dium(Ⅳ) in fresh water samples.The vanadium(Ⅳ) in the tap water, and the Yellow River have been detemined respectively with the new method. The RSD is in the range of 0.53%～1.32%, and the recovery rate is in the range of 98.6%～104.8% .It proves that the new method can be successfully applied for the determination of vanadium(Ⅳ) in fresh water samples with satisfactory results .