微波消解-化学蒸气发生-原子荧光光谱法同时测定铁矿石中的痕量砷和汞
Simultaneous Determination of Trace As and Hg in Iron Ores by Microwave Digestion-Chemical Vapor Generation-Atomic Fluorescence Spectrometry
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摘要: 采用HCl-HNO3混合酸(体积比1∶1)微波消解铁矿样品,在消解后的样品母液中直接加入硫脲-抗坏血酸,预还原五价砷为三价砷,消除铁和其他共存离子对砷、汞测定的干扰,采用化学蒸气发生-双道原子荧光光谱法同时测定铁矿石中的痕量砷和汞。结果表明5%的HCl-HNO3混合酸(体积比1∶1)、20 g/L硼氢化钾溶液能有效保证砷、汞双元素的同时测定,制备的砷、汞标准使用溶液在2~5℃下密闭保存,在245 d内具有稳定性。砷的检出限为0.085 μg/L,汞的检出限为0.008 μg/L。通过分析5个铁矿石有证标准物质,测定As的相对标准偏差为0.9%~5.5%,回收率为77.7%~105.4%,检测值与标准值吻合;测定Hg的相对标准偏差为1.1%~3.7%,回收率为86.2%~113.2%。本方法是以牺牲汞元素的检出限来实现砷、汞两元素的同时测定,是建立在砷、汞单独测定基础上的一种快速检测方法,经全国不同地区9家实验室采用5个标准样品进行协同实验验证,能够满足日常分析要求。Abstract: A new method is described for the simultaneous determination of trace As and Hg in iron ores by microwave-assisted digestion-Chemical Vapor Generation-Atomic Fluorescence Spectrometry. Samples were dissolved by 50% HCl-HNO3 mixed acids (V∶V=1∶1). The mixed solution of thiourea and ascorbic acid was directly added to the digestion solution in order to pre-reduce As from the pentavalent state to the trivalent state and eliminate interferences caused by iron ions and other coexisting ions. The results indicate that the effective determination can be obtained simultaneously for trace As and Hg in 5% HCl-HNO3 mixed acid (V∶V=1∶1) and 20 g/L KBH4 solution. As and Hg standard mixture solution with the concentration of ρ(As)=1000 μg/L and ρ(Hg)=20 μg/L was preserved in sealed condition (2-5℃) and stable in 245 days. The proposed method was applied to analyze the concentrations of As and Hg in five certified reference materials with satisfactory results. The detection limits of As and Hg were 0.085 μg/L and 0.008 μg/L, respectively. The RSDs of As were 0.9%-5.5% and recoveries were 77.7%-105.4%. The RSDs of Hg were 1.1%-3.7% and recoveries were 86.2%-113.2%. Collaborative experiments were carried out by 9 laboratories from different areas using 5 certified reference materials. This method gives a rapid simultaneous determination for both As and Hg which is based on methods of determination of As and Hg separately and reduces the detection limit of Hg. The low cost and easy operation of the method make it attractive for routine analysis of trace As and Hg in iron ores.
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