Determination of methylmercury in biological samples and sediments by capillary gas chromatography coupled with atomic absorption spectrometry after hydride derivatization and solid phase microextraction

Abstract

A method for the extraction and determination of methylmercury in biological samples and sediments by solid phase microextraction (SPME) combined 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 headspace vial prior to extraction. A laboratory-assembled SPME device including a capillary fused-silica fiber and a modified microsyringe was used throughout the experiment. The extraction is an equilibrium process that depends on the methylmercury hydride partitioning between the liquid phase and the fiber. When the equilibrium was reached, the fiber was directly transferred to a GC column by means of the microsyringe, where the analyte was thermally desorbed inside a heated injector and subsequently the column effluent was atomized by a heated stainless steel tube and detected by an on-line coupled AAS. Several factors affecting the SPME procedure such as fiber pretreatment with hydrofluoric acid, pH buffering, addition of salt and sampling time have been investigated and optimized. The reproducibility of the SPME procedure was 91% and the detection limit based on the signal equal to 3 times the baseline noise, was 26 ng. The method was applied to determination of methylmercury in biological samples and sediments.