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 (NaBEt4), 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+), <d.l. to 92 ng g−1 (MBT), 27 to 140 ng g−1 (DBT) and 39 to 1307 ng g−1 (TBT) were found.