DETERMINATION OF METHYLMERCURY IN BIOLOGICAL SAMPLES AND SEDIMENTS BYCAPILLARY GAS-CHROMATOGRAPHY COUPLED WITH ATOMIC-ABSORPTION SPECTROMETRY AFTER HYDRIDE DERIVATIZATION AND SOLID-PHASE MICROEXTRACTION

A method for the extraction and determination of methylmercury in biol ogical samples and sediments by solid phase microextraction (SPME) com bined with capillary gas chromatography-atomic absorption spectrometry (GC-AAS) has been proposed. The methylmercury chloride was converted to its hydride form by potassium tetrahydroborate (KBH4) in a closed h eadspace vial prior to extraction. A laboratory-assembled SPME device including a capillary fused-silica fiber and a modified microsyringe w as used throughout the experiment. The extraction is an equilibrium pr ocess that depends on the methylmercury hydride partitioning between t he liquid phase and the fiber. When the equilibrium was reached, the f iber was directly transferred to a GC column by means of the microsyri nge, where the analyte was thermally desorbed inside a heated injector and subsequently the column effluent was atomized by a heated stainle ss steel tube and detected by an on-line coupled AAS. Several factors affecting the SPME procedure such as fiber pretreatment with hydrofluo ric acid, pH buffering, addition of salt and sampling time have been i nvestigated and optimized. The reproducibility of the SPME procedure w as 91% and the detection limit based on the signal equal to 3 times th e baseline noise, was 26 ng. The method was applied to determination o f methylmercury in biological samples and sediments.