Development, research and validation of environmental speciation methods: Evaluation by speciated isotope dilution mass spectrometry in mercury and chromium speciation analysis.

摘要

The toxicity of an element depends upon its chemical forms, which also gives vital information for samples and their relevance. A sequential extraction method for mercury speciation in soil and sediments was established based on the mobility and toxicity of different mercury species and was proposed as a draft US EPA Method 3200. In order to finalize the method, an interlaboratory validation study was performed, and the final results verified the applicability of the method. Some of the widely used mercury speciation methods were evaluated during this study and the results were compared with those obtained from EPA draft Method 3200. The performances of these methods were also tested by using SIDMS technique (EPA Method 6800) as a diagnostic tool. A highly pure isotopically labeled methylmercury (CH3201Hg+) was synthesized from commercially available isotopically enriched inorganic mercury (201HgO) and tetramethyltin with a yield of more than 90% in a synthesis procedure lasting less than 1.5 h at 60°C; the product was characterized using ICP-MS during this study.;A simple and fast closed-vessel microwave-assisted extraction method based on acidic extractant has been developed for mercury speciation from soils and sediments. The optimized sample preparation was achieved in a closed-vessel system by heating 1.0 g of sample in 10.0 mL of 4.0 M HNO3 for 10 min at 100°C with magnetic stirring. During this study, not only the SIDMS technique was established and validated for the first time for mercury speciation analysis but also a set of generic equations for one, two and three species systems in terms of unidirectional and bidirectional transformations have been developed. The modified SIDMS technique was used for the speciation of chromium from road construction materials, soils and sediments by applying microwave-assisted alkaline extraction instead of hot-plate extraction, and was observed that these matrices contain 30--70 times more Cr(VI) compared to the US EPA threshold limit (5 mg/L). This dissertation investigates and provides solution to some difficulties associated with the analyses of mercury and chromium species. The techniques developed and tested here are being adopted worldwide to assist with species related problems.