Investigation of headspace and solvent extraction methods for the determination of dimethyl- and monomethylmercury in environmental matrices

Aqueous distillation is a common initial step in the determination of monomethyl mercury (MMHg) in a variety of matrices. However, recently it was observed that during distillation, MMHg may be generated from inorganic mercury and induce in some cases significant analytical errors. Therefore we investigated a number of alternative analytical techniques for the determination of MMHg in sediments and biological tissues: (1) headspace-GC-AFS and some variants; (2) acid extraction-solvent extraction-GC-AFS; (3) acid extraction-solvent extraction-GC-ECD. Methods (2) and (3) showed MMHg generation when an inorganic Hg spike was added to the sediment sample. The headspace method yielded MMHg results in agreement with the reference values for biological and sediment reference materials. In some cases, however, the detection limit of the headspace method is not low enough for the analysis of uncontaminated samples; therefore an additional preconcentration step is required. In addition, the headspace method appeared to be particularly suited for the determination of dimethylmercury in sediments. At this stage, a limited number of samples and matrices only have been analyzed. For those, no generation of monomethylmercury nor dimethylmercury was observed until now with the headspace method.