Simultaneous Determination of Trace As and Hg in Iron Ores by Microwave Digestion-Chemical Vapor Generation-Atomic Fluorescence Spectrometry

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.