ULTRASOUND-ASSISTED THIOUREA LEACHING OF METHYLMERCURY FROM SEDIMENTSFOR GAS-CHROMATOGRAPHY ION-TRAP MASS-SPECTROMETRIC ANALYSIS

A simple and selective method was established for the teaching of meth ylmercury (MeHg) from river sediments. Spiked sediment samples were ex tracted with 0.50% m/v thiourea aqueous solution by sonication extract ion. The effect of various conditions on the extraction efficiency, in cluding thiourea concentration, leaching time and liquid-to-solid rati o (L/S) was studied Optimal conditions for MeHg extraction were with a n 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 direct ly subjected to derivatization/extraction with sodium tetraphenylborat e, followed by preconcentration and gas chromatography/ion trap mass s pectrometric (GC/ITMS) analysis. The ultrasound-assisted thiourea leac hing and common HCl leaching procedure were compared. The former one y ields MeHg recoveries comparable with those obtained by HCl leaching p rocedure (56%). The incomplete recovery suggests the strong binding of MeHg to some sediment components such as sulfides or selenides. The u ltrasound-assisted leaching procedure is an attractive alternative to the HCl procedure because of its rapid speed the capability of providi ng a more clean extract and the absence of degradation reactions.