Study on Simultaneous and Rapid Analysis Method of X-Ray Fluorescence Spectrum for Determination of Chromium, Cadmium and Lead in Water

Coprecipitation method was adopted for simultaneous enrichment Cr, Cd and Pb in water by using sodium hydroxide and sodium sulfide as precipitant. The precipitation homogeneous suspension of Cr(OH)3, Cd(OH)2 and PbS was filtered to prepare uniform Cr, Cd and Pb thin film samples. The energy dispersive XRF spectra of thin film samples were measured in order to realise simultaneous and rapid analysis and determination of Cr, Cd and Pb in water. The influence of reaction time and molar ratio of reactants in the process of enrichment to the XRF spectrum intensity of thin film samples was studied. The precipitation reaction time for 5 min, the best mole ratios of OH- with Cr3+ for 5. 0, OH- with Cd2+ for 5. 0, and S2- with Pb2+ for 2. 0 were the optimum reaction conditions, The homogeneity of thin film samples with different concentrations after enrichment was tested. All the relative standard deviations of fluorescence intensity at six different positions at enrichment area were less than 4.8% a which indicates that all the thin film samples are in good uniformity, The theoretical concentration of thin film samyypies with different concentrations was compared with measured concentration with ICP-MS method, which confirms that the enrichment rate of this enrichment method for Cr, Cd and Pb in water can reach more than 90%. According to the fluorescence intensity of the thin film samples and the concentration measurements with ICP-MS, the quantitative analysis method of X-ray fluorescence spectrum for Cr, Cd and Pb in water based on the above enrichment was established. The linear correlation coefficients of Cr, Cd and Pb calibration curve were 0. 997 3, 0. 995 0 and 0. 999 8, respectively. When the volume of actually collecting water sample for 50ml, the detection limits of Cr, Cd and Pb were 7. 4, 29. 6 and 8. 5 mu g . L-1, respectively. All the detection limits are lower than the maximum allowable emission concentration of Cr, Cd and Pb in (Integrated wastewater discharge standard GB 8978-1996). So this method can realize the simultaneous and rapid analysis and determination of Cr, Cd and Pb in the discharged wastewater of industrial production and life. This study provides a basis for simultaneous and rapid on-line monitoring of a variety of heavy metals in water for X-ray fluorescence spectrometry.