Fast method for routine simultaneous analysis of methylmercury and butyltins in seafood

A simple, fast, and accurate method for the simultaneous determination of methylmercury (MeHg(+)), monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) in seafood is proposed. The method makes use of relatively cheap instrumentation and allows simultaneous analysis of those four species in a routine basis. The sample is treated with methanolic potassium hydroxide in an ultrasound bath, derivatised with sodium tetraethylborate (NaBEt(4)), preconcentrated into n-hexane and analysed by gas chromatography with atomic emission detection (GC-MIP/AES). The soft extraction conditions provided by ultrasound energy prevent chemical decomposition of the analytes and allow fast and efficient recovery of the species considered. Both the extraction and the derivatisation/preconcentration steps were optimised. Detection limits of 34, 3, 6 and 8 ng g(-1) (dry mass) were obtained for MeHg(+), MBT, DBT and TBT, respectively, using the best experimental conditions found. The uncertainty of the analysis ranged from 11% (MeHg(+)) to 15% (MBT). The accuracy of the method was checked by the analysis of several certified reference materials, e.g., BCR 477 (mussel tissue, MBT, DBT and TBT), DOLT-2 (dogfish liver, MeHg(+)), BCR 463 (tuna fish, MeHg(+)) and NIST 2976 (mussel tissue, MeHg(+)) with satisfactory results. Several oyster samples collected in the estuary of the Oka River (Urdaibai, Unesco Reserve of the Biosphere, Basque Country) during four sampling campaigns in 2003-2004 were processed following the proposed procedure. Concentrations ranging from 65 to 149 ng g(-1) (MeHg(+)),