Evaluation of some isolation methods for organomercury determination in soil and fish samples by capillary gas chromatography - Atomic fluorescence spectrometry

Three extraction methods, acidic KBr/CuSO4 isolation-methylene chloride extraction, acidic KBr/CuSO4 isolation-methylene chloride extraction with an alkaline digestion pretreatment, and an extraction method at a milder condition with citrate buffer and dithizone in chloroform, were studied for methylmercury and ethylmercury determination in soils, sediments and fish samples by the recently developed capillary gas chromatography-atomic fluorescence spectrometry system (GC-AFS). The acidic KBr/CuSO4-methylene chloride extraction and the acidic KBr/CuSO4-methylene chloride extraction with an alkaline digestion pretreatment were shown to be the effective methods for soils/sediments and fish samples analysis, respectively. The presence of ethylmercury species in soils of the Florida Everglades, observed with the acidic KBr/CuSO4 isolation and methylene chloride extraction procedure, was further confirmed with the dithizone complexation/extraction procedure. The GC-AFS analytical method offers high sensitivity and selectivity for the determination of organomercury halides. The GC column maintenance, a critical step for organomercury halides analysis using GC is also discussed.