Ultrasound-assisted thiourea leaching of methylmercury from sediments for gas chromatography ion trap mass spectrometric analysis

Abstract

A simple and selective method was established for the teaching of methylmercury (MeHg) from river sediments. Spiked sediment samples were extracted with 0.50% 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.