Olivier F. X. Donard

A critical review of thermodynamic data for selenium species at 25°C

Abstract The accuracy of published selenium thermodynamic data was evaluated to obtain a reliable basis for modelling Se migration behaviour in contaminated areas. The Modified Bromleys Methodology was used to correct equilibrium constant to the standard state (zero ionic strength, 25°C and 1 bar pressure). Since redox reactions control the migration of selenium, equilibria between the various Se oxidation states and the associated reactions — acid–base, precipitation, and complexation — were studied. Although pKa values for H2SeO3 and H2SeO4 acid–base reactions are well known, an ambiguity exists for the second dissociation of H2Se. A value of 14 appears to be more suitable than a value close to 11.5. The most adequate standard potentials for the redox reactions of selenium are proposed. Because of the very low solubility of metal-selenides, most of their solubility product constants are derived from combination of formation thermodynamic data selected in the literature or extrapolated from those of the corresponding sulfides. Several values are reported for Se(IV) and Se(VI), but they are not always in agreement. In generally, few values have been determined recently and noticeable differences can be observed between old and recent values. For complexation reactions, there is a lack of data and for many equilibria only one constant is available.

Rapid Determination of Inorganic Mercury and Methylmercury in Biological Reference Materials by Hydride Generation, Cryofocusing, Atomic Absorption Spectrometry After Open Focused Microwave-assisted Alkaline Digestion

A rapid and simple microwave-assisted digestion method with alkaline solution (tetramethylammonium hydroxide or methanolic KOH solution) for speciation analysis of inorganic mercury and methylmercury (MeHg + ) in biological tissues was developed. Extracts with quantitative recoveries of mercury species after microwave-assisted alkaline dissolution of the sample were directly analysed by an automated on-line hyphenated system incorporating aqueous hydride generation, cryogenic trapping, gas chromatography and detection by atomic absorption spectrometry. Optimum conditions allow sample throughput to be controlled by the instrumental analysis time (≈10 min per sample) and not by the sample preparation step. At a power of 40–60 W, sample preparation time is only 2–4 min, which is much faster than previous literature methods. The proposed method was validated by the analysis of three biological certified reference materials, CRM 463, DORM-1 and TORT-1, and one BCR sample from an interlaboratory study, Tuna Fish 2. The detection limit of the overall procedure was found to be 3 ng per gram of pulverised dried biological tissue, for both labile Hg 2+ and MeHg + . After alkaline extraction, a mean recovery of 102% with a relative standard deviation of 7% was obtained for methylmercury concentrations ranging from 0.128 to 3.464 µg g -1 as Hg in the four reference fish tissues mentioned above. Total mercury, calculated as the sum of determined inorganic mercury and methylmercury, was also in agreement with the certified values. The methylmercury extraction efficiency of five extractants, viz. , nitric, hydrochloric and acetic acid, and tetramethylammonium hydroxide and methanolic KOH solution, the temperature profile of these extractants under microwave irradiation and the behaviour and stability of methylmercury in a focused microwave field were also investigated.

Analytical techniques applied to the speciation of selenium in environmental matrices

Abstract The toxicity and essential nature of Se in the environment depend on its concentration and the chemical forms in which it is present. Se and its derivatives may be widely dispersed throughout the environment as a result of anthropogenic inputs such as fossil fuel combustion and industrial, agricultural and natural processes. In order to evaluate the effects of the different Se species on living organisms, sensitive analytical methods are required for their determination in complex environmental matrices. An overview is given of the importance of Se speciation and the distribution, accumulation and transformation of the species in the environment. The state of the art of various techniques is discussed. The main sources of errors in each step involved in the analytical methods are reported and the importance of quality control and the need to use reference materials are also stressed.

Chromium speciation in solid matrices and regulation: a review

In recent years, the extensive use of chromium in industrial processes has led to the promotion of several directives and recommendations by the European Union, that try to limit and regulate the presence of Cr(VI) in the environment and to protect industrial workers using chromium and end-users of manufactured products. As a consequence, new standard methods and analytical procedures have been published at the EU level for Cr(VI) determination in soil, sludge, sediment, and similar waste materials, workplace atmospheres, cement, packaging materials, industrially produced samples, and corrosion-protection layers on some components of vehicles and electrical and electronic equipment. The objective of this article is to summarize the different directives and recommendations and to critically review the currently existing standard methods and the methods published in the literature for chromium speciation in the above mentioned solid matrices, putting the emphasis on the different extraction procedures which have been developed for each matrix. Particular attention has been paid to Cr(III) and Cr(VI) inter-conversions that can occur during extraction and efforts to minimize these unwanted reactions. Although the use of NaOH-Na2CO3 solutions with hot plate extraction seems to be the more widespread procedure, species transformation can still occur and several studies suggest that speciated isotope-dilution mass spectrometry (SIDMS) could be a suitable tool for correction of these interconversions. Besides, recent studies have proved the role of Cr(III) in chromium toxicology. As a consequence, the authors suggest an update of standard methods in the near future.

Transient Pb isotopic signatures in the Western European atmosphere

The progressive phasing-out of lead from gasoline has resulted in a significant decrease in the global atmospheric lead burden over the last 20 years. Here we show that in Europe this change in lead concentration - determined by the analysis of aerosols - is accompanied by a systematic change in lead isotopic compositions and that there was a significant reversal in this trend during the 1970s. Such changes in isotopic signatures over time have been accurately documented in North America. We observe that European and North American records display opposite trends in isotopic composition, thus providing a powerful tool for assessing the response time of the North Atlantic environment and its surrounding continents to transient lead inputs

Rapid and Quantitative Microwave-assisted Recovery of Methylmercury From Standard Reference Sediments

A simple and rapid method has been developed to determine methylmercury in sediments. The procedure is based on the quantitative microwave-assisted leaching of methylmercury from sediments with an acidic extractant. Sample preparation is achieved in an open focused microwave field by heating about 1 g of dry sediment suspended into 10 ml of 2 mol l -1 HNO 3 during 3–4 min at a power of 40–60 W. The extracted mercury compounds are ethylated, cryogenically trapped in a chromatographic phase, successively eluted and detected in an electrothermally heated quartz furnace by CV AAS. The method has been validated by the analysis of the certified IAEA-356 and CRM 580 reference materials and one sediment sample, BCR S19, from an intercomparison study within the framework of a certification exercise sponsored by the Community Bureau of Reference (BCR) of the European Commission. The detection limit of the procedure is 0.5 ng of methylmercury per gram of dry sediment. After analysis of the sediments mentioned above (methylmercury ranging from 5 to 80 ng g -1 ), a mean methylmercury recovery of 97% and an RSD of 7% were obtained. Under optimum conditions, sample throughput is restricted by the instrumental analysis time (about 20 min per sample), rather than by the sample preparation step. In addition, the methylmercury extraction efficiency of four different acids, nitric, hydrochloric, sulfuric and acetic acid, has been investigated for comparison. Results on the behaviour and stability of methylmercury in a microwave field are also provided.

Simultaneous use of strontium:calcium and barium:calcium ratios in otoliths as markers of habitat: Application to the European eel (Anguilla anguilla) in the Adour basin, South West France

Sr:Ca and Ba:Ca ratios in water from the Adour estuary show a clear relationship with the salinity of the surrounding water for salinities <20, while ratios are almost constant above this level of salinity. A positive relationship was observed for the Sr:Ca ratio, whereas it was inverse for the Ba:Ca ratio. These two elemental ratios were measured in the otoliths of the European eels (Anguilla anguilla L.) using femtosecond laser ablation linked to an ICP-MS (fs-LA-ICP-MS). There was a direct relationship between the elemental ratios recorded in eel otoliths and those found in water from fresh and marine areas, suggesting that Sr:Ca and Ba:Ca ratios in eel otoliths can be used as markers of habitat in this estuary. Continuous profiling allowed the determination of three behaviour patterns in terms of habitat: freshwater, estuary and migratory individuals. Finally, the above results support the simultaneous use of both ratios for a better understanding of the migratory contingents and also as a relevant method to avoid a misidentification of environmental migratory history due to the presence of vaterite crystal in the otolith matrix.

Simultaneous Determination of Volatile Metal (Pb, Hg, Sn, In, Ga) and Nonmetal Species (Se, P, As) in Different Atmospheres by Cryofocusing and Detection by ICPMS

A sensitive method for multielemental speciation analysis of volatile metal and metalloid compounds in air has been developed. The analytes are sampled simultaneously in the field by cryofocusing on a small glass wool-packed column at -175 °C. Detection is performed in the laboratory by low-temperature GC hyphenated with ICPMS. Oxygen addition in the carrier gas was used to reduce interferences originating from the presence of volatile carbon-containing species in the samples. Plasma stability during analysis was monitored continuously by internal standardization (Xe). This system provides routine absolute detection limits of 0.06-0.07 pg (as Pb) for tetraalkyllead species (Me(4)Pb, Et(4)Pb), 0.2 pg (as Sn) for tetraalkyltin species (Me(4)Sn, Et(4)Sn), 0.8 pg (as Hg) for mercury species (Hg(0), Me(2)Hg, Et(2)Hg), and 2.5 pg (as Se) for selenium species (Me(2)Se). This instrumentation makes it possible to collect small air sample volumes and has been successfully applied to the determination of volatile metal and metalloid species in the atmosphere in urban and rural locations. Qualitative application in the semiconductor industry is also reported with regard to the detection of arsenic (ASH(3), tert-butylarsine), phosphorus (PH(3), tert-butylphosphine), alkylindium, and gallium species.

Simultaneous Determination of Species-Specific Isotopic Composition of Hg by Gas Chromatography Coupled to Multicollector ICPMS

This work presents the simultaneous online determination of the isotopic composition of different Hg species in a single sample by the hyphenation of gas chromatography (GC) with multicollector-inductively coupled plasma mass spectrometry (MC-ICPMS). With the use of commercially available instrumentation, precise and accurate species-specific Hg isotope delta values (per mil deviation of the Hg isotope ratio in the sample relative to a reference standard) have been obtained online from consecutive GC transient signals. The use of isothermal temperature programs to extend the elution of the Hg species, the proper selection of the peak integration window, as well as the preconcentration of real samples are critical to provide optimal counting statistics. Also, isotope ratio drift during transient signal elution was overcome by introducing a mixed Hg(II) and MeHg standard bracketing scheme and expressing all results using the delta-notation relative to SRM NIST-3133. Using the proposed methodology, we have obtained an external 2SD precision of 0.56 per thousand for delta (202)Hg that is more than 10 times smaller than the overall Hg stable isotope variation thus far observed in terrestrial samples. The measurement of species-specific Hg isotopic composition relative to SRM NIST-3133 has been validated versus two other analytical techniques, i.e., conventional nebulization (CN) of Hg(II) solution and cold vapor (CV) generation of Hg (0) vapor. A good agreement between the species-specific delta values obtained by the different techniques has been obtained in secondary fractionated reference standard (UM-Almaden) and environmental matrixes, i.e., BCR-CRM 464 (tuna fish) and IAEA-085 (human hair). The results show mass-dependent and mass-independent fractionation in environmental samples, i.e., mass-independent fractionation of odd isotopes (199)Hg and (201)Hg in tuna fish was observed. This methodology provides new possibilities for the future study of species-specific stable isotope geochemistry of Hg and other trace metals.

Determination of palladium, platinum and rhodium concentrations in urban road sediments by laser ablation-ICP-MS

The introduction of catalytic converter technology to cars has alleviated gaseous exhaust emissions but in turn has resulted in emissions of the three platinum group metals (PGMs), Pd, Pt and Rh, contained in the automobile catalyst. The environmental effects of PGMs are still largely unknown and their accurate determination is particularly difficult because concentrations are at trace levels. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a direct trace element measurement technique and can be used for the rapid characterization of metals in solid environmental matrices. Here, the capability of LA-ICP-MS for the direct quantitative determination of PGMs in road sediments was assessed. Two Nd:YAG laser systems operating at 266 and 1064 nm, respectively, were coupled to an ICP-MS. Uncontaminated road sediments were spiked with PGMs, both as solution and as solid certified reference material, and used to assess the analytical performance of the technique and to calibrate the instrument. Interferences due to the formation of molecular ions and double charged ions were investigated. The LA-ICP-MS was then used to determine the concentration of PGMs in a recent urban road sediment and the results were compared with high resolution-ICP-MS measurements after microwave sample digestion with Aqua Regia. The LA-ICP-MS allows the quantitative analysis of Pd, Pt, and Rh in road sediments at sub microgram per gram levels with a relative standard deviation of 10% and with estimated detection limits in the lower nanogram per gram range. Good agreement between LA-ICP-MS and HR-ICP-MS analysis could be obtained for Pt and Rh (<3% R.S.D. at ca. 100 ng g−1) whereas the determination of Pd remains subject to interferences.