Speciation of organomercurials in biological and environmental samples by gas chromatography with microwave-induced plasma atomic emission detection

Speciation of mercury in soil and sediment by selective solvent and acid extraction

In order to characterize the mercury hazard in soil, a sequential extraction scheme has been developed to classify mercury species based on their environmental mobility and/or toxicity for either routine lab analysis or on-site screening purposes. The alkyl mercury species and soluble inorganic species that contribute to the major portion of potential mercury toxicity in the soil are extracted by an acidic ethanol solution (2% HCl+10% ethanol solution) from soil matrices as "mobile and toxic" species. A High-Performance Liquid Chromatography (HPLC) system coupled with Inductively Coupled Plasma Mass Spectrometry (ICP-MS) detection has been developed to further resolve the species information into soluble inorganic species (Hg(2+)), methylmercury(II) (MeHg(+)) and ethylmercury(II) (EtHg(+)) species. Alternatively, these species can be separated into "soluble inorganic mercury" and "alkyl mercury" sub-categories by Solid-Phase Extraction (SPE). A custom Sulfydryl Cotton Fiber (SCF) material is used as the solid phase medium. Optimization of the SCF SPE technique is discussed. Combined with a direct mercury analyzer (DMA-80), the SCF SPE technique is a promising candidate for on-site screening purposes. Following the ethanol extraction, the inorganic mercury species remaining in soil are further divided into "semi-mobile" and "non-mobile" sub-categories by sequential acid extractions. The "semi-mobile" mercury species include mainly elemental mercury (Hg) and mercury-metal amalgams. The non-mobile mercury species mainly include mercuric sulfide (HgS) and mercurous chloride (Hg(2)Cl(2)).

Determination of methylmercury in human hair by ethylation followed by headspace solid-phase microextraction-gas chromatography-cold-vapour atomic fluorescence spectrometry

An analytical procedure for the determination of methylmercury in human hair after acid digestion using aqueous ethylation, headspace solid-phase microextraction sampling and final gas chromatography-cold-vapour atomic fluorescence spectrometry detection is described. Acid digestion, extraction procedure and chromatographic conditions were optimised. An optimal linear range using standard mercury solutions was found and concentration detection limits for the mercury species, MeHg and Hg2+, were about 50 and 80 ng/g, respectively, for 100 mg of human hair. The reproducibility of the developed analytical procedure assessed for hair samples with incurred MeHg was better than 18% (n=5). A certified reference material from the National Institute of Environmental Studies (Japan) was used for validation. Analysis of human hair collected from urban inhabitants was performed and the mean value of methylmercury content in hair samples was 0.764 +/- 0.732 microg/g for the population tested. The developed analytical method is simple, fast and a suitable procedure for the monitoring and screening of human exposure to methylmercury.

Methylmercury determination in biological samples by derivatization, solid-phase microextraction and gas chromatography with microwave-induced plasma atomic emission spectrometry

A method for the extraction and gas chromatographic determination of methylmercury in biological matrices is presented. By combining the advantages of two extraction techniques-microwave-assisted extraction (MAE) and solid-phase microextraction (SPME)--the separation of methylmercury from biological samples is possible. Specifically, the procedure involves microwave extraction with 3 M hydrochloric acid, followed by aqueous-phase derivatization with sodium tetraphenylborate and headspace SPME with a silica fibre coated with polydimethylsiloxane (PDMS). For optimization of the derivatization-SPME procedure, a central composite experimental design with alpha = 1.682 and two central points was used to model gas-chromatographic peak areas as functions of pH, extraction temperature and sorption time. A desirability function was then used for the simultaneous optimization for methylmercury and Hg(II). The optimal derivatization-SPME conditions identified were close to pH 5, temperature 100 degrees C, and sorption time 15 min. The identification and quantification of the extracted methylmercury is carried out by gas chromatography with microwave-induced plasma atomic emission spectrometry detection. The validity of the new procedure is shown by the results of analyses of certified reference materials.

Experimental design of a microwave-assisted extraction-derivatization method for the analysis of methylmercury

A simultaneous microwave-assisted extraction-derivatization procedure was developed and optimized for methylmercury analysis from biological samples. The analyte was derivatized with sodium tetraphenylborate forming a more hydrophobic compound, methylphenylmercury, which was extractable in toluene. The microwave extraction-derivatization procedure was optimized using experimental design, 2(5-1) fractional factorial. This chemometrical approach considers main effects as well as interactions of the influential parameters, indicating that temperature and its interaction with NaBPh4 and acetic acid volumes were the variables that significantly affected methylmercury recoveries.

Application of chromatographic and electrophoretic methodology to the speciation of organomercury compounds in food analysis

Trace metals such as mercury, especially its organic compounds, are an important risk to the environment and to man due to their accumulation in the food chain. For this reason, the routine determination of the very toxic methylmercury, and of other organic and inorganic mercury compounds in marine and land animals, vegetables, fruits and fresh water is of increasing importance in health and environmental control programmes throughout the world. The majority of speciation methods for organomercurials involve a series of fundamental steps for the identification and quantification of samples of biological origin: extraction or isolation from the matrix; derivatisation and concentration; detection; separation of different species of interest and of interference. Each of these steps, as part of the chromatographic analysis of MeHg and of other organomercurials is revised in this study using food samples.