Speciation analysis of mercury in cereals by liquid chromatography chemical vapor generation inductively coupled plasma-mass spectrometry

A simple and rapid procedure for the separation and determination of inorganic, methyl, and ethyl mercury compounds was described using liquid chromatography (LC) followed by vapor generation inductively coupled plasma-mass spectrometry (VG-ICP-MS). Well resolved chromatograms were obtained within 5 min by reversed-phase liquid chromatography with a C8 column as the stationary phase and a pH 4.7 solution containing 0.5% v/v 2-mercaptoethanol and 5% v/v methanol as the mobile phase. The separated mercury compounds were converted to mercury vapors by an in situ nebulizer/vapor generation system for their introduction into ICP. The concentrations of NaBH4 and HNO3 required for vapor generation were also optimized. The method was applied for the speciation of mercury in reference materials NIST SRM 1568a Rice Flour and NIST SRM 1567a Wheat Flour and also rice flour and wheat flour samples purchased locally. The accuracy of the procedure was verified by analyzing the certified reference material NRCC DOLT-3 Dogfish Liver for methyl mercury. Precision between sample replicates was better than 13% for all the determinations. The detection limits of the mercury compounds studied were in the range 0.003-0.006 ng Hg mL(-1) in the injected solutions, which correspond to 0.02-0.06 ng g(-1) in original flour samples. A microwave-assisted extraction procedure was adopted for the extraction of mercury compounds from rice flour, wheat flour, and fish samples using a mobile phase solution.