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 monom ethyl mercury (MMHg) in a variety of matrices. However, recently it was obs erved that during distillation, MMHg may be generated from inorganic mercur y and induce in some cases significant analytical errors. Therefore we inve stigated a number of alternative analytical techniques for the determinatio n of MMHg in sediments and biological tissues: (1) headspace-GC-AFS and som e variants; (2) acid extraction-solvent extraction-GC-AFS; (3) acid extract ion-solvent extraction-GC-ECD. Methods (2) and (3) showed MMHg generation w hen an inorganic Hg spike was added to the sediment sample. The headspace m ethod yielded MMHg results in agreement with the reference values for biolo gical and sediment reference materials. In some cases, however, the detecti on limit of the headspace method is not low enough for the analysis of unco ntaminated samples; therefore an additional preconcentration step is requir ed. In addition, the headspace method appeared to be particularly suited fo r the determination of dimethylmercury in sediments. At this stage, a limit ed number of samples and matrices only have been analyzed. For those, no ge neration of monomethylmercury nor dimethylmercury was observed until now wi th the headspace method. (C) 1999 Elsevier Science Ltd. All rights reserved .