On the reliability of methods for the speciation of mercury based on chromatographic separation coupled to atomic spectrometric detection

This thesis deals with the reliability of methods for the speciation of mercury in environmental and biological samples. Problems with speciation methods that couple chromatography to atomic spectrometric detection and how to overcome the problems are discussed. Analytical techniques primarily studied and evaluated are high performance liquid chromatography-cold vapour-atomic absorption spectrometry (HPLC-CV-AAS), HPLC-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS), capillary electrophoresis-ICP-MS (CE-ICP-MS) and gas chromatography-ICP-MS (GC-ICP-MS). Applying a multi-capillary approach increased the analyte amount injected into a CE-ICP-MS system and improved the overall sensitivity. A microconcentric nebulizer with a cyclone spray chamber was shown to improve the detection limits for mercury species 3-13 times in HPLC-ICP-MS and 11-19 times in CE-ICP-MS compared to a cross-flow nebulizer with a Scott spray chamber. To decrease the interference of water vapour in HPLC-CV-AAS a Nafion dryer tube was inserted between the CV-generation and the detector. Methyl mercury was however lost in the Nafion unless it was reduced to elemental mercury prior transport through the dryer tube. During sample pre-treatment, incomplete extraction, losses and transformation (alkylation, dealkylation, oxidation and reduction) of mercury species can lead to significant errors (underestimation and overestimation) in the determination of the concentrations. Methods to detect and determine the degree of transformation as well as correct for errors caused by transformation are presented in the thesis. The preferable method use species-specific enriched stable isotope standards in combination with MS detection and a matrix based calculation scheme. This approach is very powerful as both the concentrations of the species as well as the degrees of transformation can be determined within each individual sample