Ultrasound-Assisted Thiourea Leaching of Methylmercury from Sediments for Gas Chromatography/Ion Trap Mass Spectrometric Analysis

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Abstract
A simple and selective method was established for the leaching of methylmercury (MeHg) from river sediments. Spiked sediment samples were extracted with 0.5% m/v thiourea aqueous solution by sonication extraction. The effect of various conditions on the extraction efficiency, including thiourea concentration, leaching time and liquid-to-solid ratio (L/S) was studied. Optimal conditions for MeHg extraction were with an aqueous thiourea solution of 0.5% m/v, leaching time of 50 min, and liquid-to-solid ratio of 8/1. The leach solutions obtained were directly subjected to derivatization/extraction with sodium tetraphenylborate, followed by preconcentration and gas chromatography/ion trap mass spectrometric (GC/ITMS) analysis. The ultrasound-assisted thiourea leaching and common HCl leaching procedure were compared. The former one yields MeHg recoveries comparable with those obtained by HCl leaching procedure (56%). The incomplete recovery suggests the strong binding of MeHg to some sediment components such as sulfides or selenides. The ultrasound-assisted leaching procedure is an attractive alternative to the HCl procedure because of its rapid speed, the capability of providing a more clean extract, and the absence of degradation reactions.

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