Study And Application Of Determination Of Trace Nickel (Ⅱ) In Water By The Catalytic Kinetic Spectrophotometric Method

Nickel is considered as an essential micronutrient element. It is very meaningful to know about the content and distribution of nickel (Ⅱ) in water for environmental science, chemical oceanography and biogeochemistry research. At present, the most determination methods of nickel (Ⅱ) in water can be used only after preliminary treatment. However, these operation procedures are very tedious. The methods which can analyze nickel (Ⅱ) in seawater directly are seldom reported.The catalytic dynamic analytic method which has higher sensitivity, low detection limit, simple operation has developed rapidly. Thus, based on the catalytic kinetic theory new response systems and response mechanisms to determine the concentration of nickel (Ⅱ) has been studied. More sensitive and higher selective catalytic kinetic methods for the determination of nickel (Ⅱ) in fresh water and seawater samples need to be established.In this study, firstly, a new method for the determination of trace nickel (Ⅱ) by the catalytic kinetic spectrophotometric method has been studied. The new established methods can determine the concentration of nickel (Ⅱ) in fresh water and seawater samples. The kinetic parameters of the reactions of nickel (Ⅱ) are also discussed. On this base, this study also establishes a new catalytic dynamic analytic method to determine simultaneously double components of nickel (Ⅱ) and iron (Ⅲ) based on CPA matrix method. And the method is applied in fresh water.The main results of the research are as follows:1 A new catalytic kinetic spectrophotometric method has been developed for the determination of trace nickel (Ⅱ). The reaction system is found for determining trace nickel (Ⅱ) using RAWL as indicator and potassium periodate as oxidant. The results of the orthogonal experiments and the single factor experiments of nickel (Ⅱ) show that the analytical conditions are:pH= 2.00, cRAWL= 5.00×10-5 mol·L-1, cKIO4=2.00×10-5 mol·L-1, reaction time t=10.00min and reaction temperature T=25.0℃. The relative standard deviations of the proposed method are in the range of 0.52%-2.49%. The limit of detection is 1.70 ng·mL-1. The method allows the measurement of nickel (Ⅱ) in the range of 0-60.00 ng·mL-1. Moreover, the experiments show most cations and anions do not interfere with the measurement of nickel (Ⅱ) under the analytical condition. The nickel (Ⅱ) in the tap water samples and the Yellow River samples are determined respectively with the new method. The relative standard deviations are in the range of 0.43%～1.28% and the recovery efficiencies are in the range of 98.0%～101.3%. The proposed method has obvious advantages, such as high precision, low detection limit, large range of linearity. This method can operate at room temperature compared with existing catalytic kinetic spectrophotometric method.2 The catalytic kinetic equation can be written as:-(dcR)/(dt)=KcRcK1/4cNi. The apparent activation energy of the reaction is found to be 39.97 kJ·mol-1 and the apparent reaction rate constant is 0.0131 min-1.3 This paper finds out that there is a obviously different phenomenon between in seawater medium and in the fresh water system. Put forward a calibration method of the standard addition method for this phenomenon. This calibration method is used to determine the nickel (Ⅱ) in seawater samples. The nickel (Ⅱ) concentrations in the surface seawater of 11 sites in Qingdao offshore are determined and the level distribution map of nickel (Ⅱ) is drawn.4 A new catalytic kinetic spectrophotometric method has been studied based on CPA matrix method. And this method is applied in the simultaneous determination of double components of nickel (Ⅱ) and iron (Ⅲ) in fresh water samples. The proposed method allows the measurement of nickel (Ⅱ) in the range of 0～60.00 ng·mL-1 and iron (Ⅲ) in the range of 0～70.00 ng·mL-1. The relative standard deviations of the method are in the range of 0.37%-2.32%. The method is used for the determination of nickel (Ⅱ) and iron (Ⅲ) binary mixture in a range of 5.00～60.00 ng·mL-1. The accuracies in determining the standard nickel (Ⅱ) and iron (Ⅲ) solution are in the range of 95.4%-107.7%. The nickel (Ⅱ) and iron (Ⅲ) in the tap water samples and the Yellow River samples are determined respectively with the new method. The relative standard deviations of the results are in the range of 0.47%～1.60% and the recovery efficiencies are in the range of 95.5%-99.0%.