RAPID AND QUANTITATIVE MICROWAVE-ASSISTED RECOVERY OF METHYLMERCURY FROM STANDARD REFERENCE SEDIMENTS

A simple and rapid method has been developed to determine methylmercur y in sediments, The procedure is based on the quantitative microwave-a ssisted leaching of methylmercury from sediments with an acidic extrac tant. Sample preparation is achieved in an open focused microwave fiel d by heating about 1 g of dry sediment suspended into 10 ml of 2 mol l (-1) HNO3 during 3-4 min at a power of 40-60 W. The extracted mercury compounds are ethylated, cryogenically trapped in a chromatographic ph ase, successively eluted and detected in an electrothermally heated qu artz furnace by CV AAS, The method has been validated by the analysis of the certified IAEA-356 and CRM 580 reference materials and one sedi ment sample, BCR S19, from an intercomparison study within the framewo rk of a certification exercise sponsored by the Community Bureau of Re ference (BCR) of the European Commission, The detection limit of the p rocedure is 0.5 ng of methylmercury per gram of dry sediment, After an alysis of the sediments mentioned above (methylmercury ranging from 5 to 80 ng g(-1)), a mean methylmercury recovery of 97% and an RSD of 7% mere obtained, Under optimum conditions, sample throughput is restric ted by the instrumental analysis time (about 20 min per sample), rathe r than by the sample preparation step, In addition, the methylmercury extraction efficiency of four different acids, nitric, hydrochloric, s ulfuric and acetic acid, has been investigated for comparison, Results on the behaviour and stability of methylmercury in a microwave field are also provided.