Mercury in environmental samples: Speciation, artifacts and validation

Abstract

Speciation of mercury compounds in environmental samples requires rigorous analytical procedures at each stage of sample collection, treatment and measurement. Sampling, the first step, is generally only critical for water samples. The best materials for water-sample storage and processing are Pyrex and Teflon (PTFE or FEP) after a severe cleaning procedure. Extraction of the Hg species from its matrix, the second step, requires an aggressive treatment, such as acid extraction (mostly combined with solvent extraction), distillation or alkaline extraction. Extraction is one of the most critical steps, and, for biota and sediments, almost certainly the most critical, because two conflicting issues need to be addressed – obtaining adequate recovery, and preventing losses. Extraction efficiency and validation are discussed as well as methylation artifacts, especially when the distillation method is applied to sediments. Separation of the Hg species, the third step, includes derivatization followed by gas chromatography (GC), new GC improvements and liquid chromatography (LC), which has, since the development of more sensitive detectors, resulted in wider applications in environmental studies. Detection of the Hg species is the fourth and last step in the analytical procedure. The development of commercial, relatively inexpensive, extremely sensitive, selective cold vapor atomic fluorescence spectrometry (CV-AFS) instrumentation in the late 1980s and 1990s made this the most popular detector for the laboratories working on the biogeochemical cycling of Hg. In recent years, the use of inductively coupled plasma mass spectrometry (ICP-MS) in speciation analysis has increased tremendously. Besides its high sensitivity and selectivity, ICP-MS offers the opportunity to perform speciated isotope dilution mass spectrometry (SID-MS). Finally, as other measurement fields, speciation analysis requires suitable reference materials to be available for the verification of accuracy and to meet quality-assurance needs. We also address these important aspects.