Study And Application Of Determination Of Trace Chromium (â…¥) In Water By The Catalytic Kinetic Spectrophotometric Method

Chromium (Ⅵ) is considered as a kind of important environmental pollutant, It is very meaningful to be aware of the content and distribution of chromium (Ⅵ) in water for chemical oceanography, environmental monitoring and protection. At present, the determination methods of vanadium in water can be used only after the preliminary treatment and preconcentration. The operations are very tedious, the analysis cost is high and there are many interference factors. The method can be directly used to the determination of trace chromium (Ⅵ) in seawater is relatively rare.The catalytic dynamic analytic method which has higher sensitivity, low detection limit, and simple operation has been developed rapidly. Therefore, based on the catalytic kinetic theory new response systems and mechanisms to determine the concentration of trace chromium (Ⅵ) has been studied. More sensitive and higher selective catalytic kinetic methods for the determination of trace chromium (Ⅵ) in water samples need to be established.In this study, a new method about determining the content of trace chromium (Ⅵ) by the catalytic kinetic spectrophotometric method has been studied, a new reaction system has been established. The kinetic parameters of the reactions of chromium (Ⅵ) are also discussed. Through the research, the new method can be used for the immediate determination of trace amount of chromium (Ⅵ) in fresh water and seawater with satisfying results.The main achievements of the research are as follows:1 A new kinetic spectrophotometric method is developed for the measurement of trace chromium (Ⅵ) in fresh water and seawater. The new reaction system is established to the determining the content of trace chromium (Ⅵ) using RAWL as indicator, CTMAB as activation reagent and potassium bromate as oxidant. The proposed method owns fairly good sensitivity and selectivity, simplicity, cheapness, low detection limit and rapidity under the lower temperature.2 The results from the orthogonal experiments and the single factor experiments of chromium (VI) show that the optimal experimental conditions are as following:pH =1.50, c(RAWL)=1.000×10-44mol/L, c (KBrO3)= 7.200×10-3 mol/L,t= 2.0min, θ=45.0℃, ρ (CTMAB)= 2.500 g/L.3 Under the optimum conditions, the proposed method allows the measurement of chromium (Ⅵ) in a range of 0～16.00 ng/mL with a detection limit of down to 0.45 ng/mL. The RSD is in a range of 0.97%～1.92%, and the recovery efficiency about measuring the standard chromium (Ⅵ) solution is in a range of 98.8%～101.5%. Moreover, it is found that most cations and anions do not interfere with the determination of trace chromium (Ⅵ) under the analytical condition..4 In the research, the kinetic parameters of reaction are studied and the mechanism of the reaction is investigated. On the basis of these values the kinetic equation of chromium (Ⅵ) can be written as:-dcR/dt=K2cRcK1/2cCr(Ⅵ)cN1/2.The apparent activation energy of the reaction is found to be 167.67kJ/mol and the apparent reaction rate constant is 0.0131 min-1.5 The new method has been applied for the determination of trace chromium (Ⅵ) in the fresh water samples successfully. The chromium (Ⅵ) in the Yellow River and Haibo River of Qingdao has been determined respectively with the new method. The RSD is in the range of 1.06%-2.63%, and the recovery rate is in the range of 99.0% ～101.5%. It proves that the new method can be successfully applied for the determination of chromium (Ⅵ) in the fresh water sample with satisfactory results.6 The new method has been applied for the determination of trace chromium (Ⅵ) in seawater samples successfully. The chromium (Ⅵ) in Qingdao offshore and Jiaozhou Bay of Qingdao has been determined respectively with the new method. The RSD is in the range of 0.41%～2.53%, and the recovery rate is in the range of 99.1%～ 100.8%. It proves that the new method can be successfully applied for the determination of chromium (Ⅵ) in seawater samples with satisfactory results.7 The concentration of Chromium (Ⅵ) in the seawater of Qingdao offshore and Jiaozhou Bay is determined using the method and the relative distribution map of chromium (VI) is drawn up. The distribution of the chromium (VI) is also discussed.