Evaluation of a purge-and-trap injection system for capillary gas chromatography-microwave induced plasma-atomic emission spectrometry for the determination of volatile selenium compounds in water

A method is presented for the selective determination of the volatile selenium species dimethylselenide and dimethyldiselenide, using a commercially available purge-and-trap injection system coupled to capillary gas chromatography-microwave induced plasma-atomic emission spectrometry. The efficiency of the purging step was evaluated and the parameters affecting the purge and trap processes were optimized. The method was applied to the determination of volatile selenium compounds in lake water. Relative detection limits of 2ng/l for dimethylselenide and dimethyldiselenide, corresponding to an absolute detection limit of 10 pg, were achieved.     

Arsenic Speciation in As(III)- and As(V)-Treated Soil Using XANES Spectroscopy

Arsenic (As) is a toxic trace element that occurs naturally in groundwater and soils. Understanding the reactions of arsenite (As(III)) and arsenate (As(V)) with soil and mineral surfaces is critical for predicting the fate and transport of As in the environment and developing better ways to remediate As-contaminated areas. This investigation uses X-ray absorption near edge spectroscopy (XANES) to evaluate the solid phase oxidation state and mineral surface binding sites in three agricultural soil samples from California, USA by fitting linear combinations of XANES spectra derived from several synthetic and well characterized As(III)- and As(V)-treated model compounds (Fe and Al metal hydroxides and aluminosilicate illite clay mineral). The results suggest that As(III) is either partially or completely oxidized to As(V) when reacted with soil in an aqueous, batch reaction. The As(III)-treated Aiken soil was composed of 60% As(III) attached to surfaces similar to lepidocrocite (γ-FeOOH)) and 40% As(V) attached to aluminosilicate (illite). The Fallbrook soil completely oxidized As(III) and the product was As(V) adsorbed on Al hydroxide (gibbsite, γ-Al(OH)₃) (62%), illite (16%), and lepidocrocite (γ-FeOOH) (22%). The reaction of As(III) with Wyo soil resulted in 42% As(III) adsorbed on surface similar to goethite and 58% As(V) adsorbed on lepidocrocite. Arsenic(V) adsorption on soil resulted in stable As(V) surface complexes that were well described by XANES spectra from As(V) adsorption complexes on gibbsite, illite, and lepidocrocite.     

Development of a mild mercaptoethanol extraction method for determination of mercury species in biological samples by HPLC–ICP-MS

A mild, efficient and convenient extraction method of using 2-mercaptoethanol contained extractant solution combined with an incubator shaker for determination of mercury species in biological samples by HPLC–ICP-MS has been developed. The effects of the concentration of 2-mercaptoethanol, the composition of the extractant solution and the shaking time on the efficiency of mercury extraction were evaluated. The optimization experiments indicated that the quantitative extraction of mercury species from biological samples could be achieved by using 0.1% (v/v) HCl, 0.1% (v/v) 2-mercapoethanol and 0.15% (m/v) KCl extractant solution in an incubator shaker for shaking overnight (about 12 h) at room temperature. The established method was validated by analysis of various biological certified reference materials, including NRCC DOLT-3 (dogfish liver), IAEA 436 (tuna fish), IAEA MA-B-3/TM (garfish filet), IAEA MA-M-2/TM (mussel tissue), GBW 08193 (bovine liver) and GBW 08572 (prawn). The analytical results of the reference materials were in good agreement with the certified or reference values of both methyl and total mercury, indicating that no distinguishable transformation between mercury species had occurred during the extraction and determination procedures. The limit of detection (LOD) for methyl (CH₃Hg⁺) and inorganic mercury (Hg²⁺) by the method are both as 0.2 μg L⁻¹. The relative standard deviation (R.S.D.s) for CH₃Hg⁺ and Hg²⁺ are 3.0% and 5.8%, respectively. The advantages of the developed extraction method are that (1) it is easy to operate in HPLC–ICP-MS for mercury species determination since the extracted solution can be directly injected into the HPLC column without pH adjustment and (2) the memory effect of mercury in the ICP-MS measurement system can be reduced.     

Determination of Labile Iron at Low nmol L−1 Levels in Estuarine and Coastal Waters by Anodic Stripping Voltammetry

A new method is presented for the determination of electrochemically labile iron in estuarine and coastal seawater. The method is based on differential pulse anodic stripping voltammetry (DPASV) at a rotating silver‐alloy disk electrode. The voltammetric parameters include a plating potential of ?1.5 V and an activation potential of ?5 V for 10s; the seawater is at the original sample pH. The main finding is the presence of a peak for low nmol L^?1 levels of iron at ?0.55 V ascribed to elemental iron deposited on the bare silver alloy electrode. The peak increased linearly with the iron concentration between <1 and 14 nmol L^?1 using a 900 s plating time. At higher concentrations an additional iron peak appeared at ?0.7 V which was also found to increase linearly with the iron concentration but at a higher concentration range from ca. 15 to 90 nmol L^?1 using a 300 s plating time. The second peak was ascribed to iron deposited on iron. Additions of chelating agents (EDTA and a siderophore) to seawater caused the iron peak to be masked indicating that this method is suitable for iron speciation as only the electrochemically labile fraction is determined. The detection limit was 0.3 nmol L^?1 using a 900 s plating time. The method was used to determine iron in the range of 5 to 50 nmol L^?1 in samples from the Mersey estuary near Liverpool and its potential use for in situ monitoring was demonstrated by using it to monitor labile iron (at 2–3 nmol L^?1) over a period of 4 days at 1 h intervals in coastal waters in the Trondheim fjord, Norway.     

Separation and sensitive determination of arsenic species (As/As) using the yeast-immobilized column and hydride generation in ICP–AES

Inorganic arsenic was separated using the yeast-immobilized column. Saccharomyces cerevisiae was covalently bonded unto the controlled pore glass, which showed selective preconcentration of As⁵⁺ over As³⁺. The effluent was directly connected to hydride generation (HG) to increase sensitivity. The optimum pH condition for the retainment of arsenic at the column was 7. As⁵⁺ and As³⁺ were completely separated in a few minutes with the flow rate of 1.5 ml min⁻¹. Three molars of nitric acid was adequate both for the elution of As⁵⁺ and hydride generation. The accuracy of the technique was tested with NIST SRMs. Quantitative analysis of arsenic species for herbicide, pesticide, and cigarette were performed, and the results showed good agreements with the suggested values. Yeast-immobilized column-HG-ICP showed a promising future for the arsenic speciation study.     

Method Development for the Speciation of Chromium in River and Industrial Wastewater Using GFAAS

A simple, sensitive and inexpensive method for the speciation of Cr(VI) and Cr(III) in river and industrial wastewater was developed, optimized and validated. Samples were collected, filtered and then chromium species were determined in the filtrate. In the filtrate, total Cr was determined directly by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). A portion of the filtered sample was buffered to pH 6.4, extracted with Amberlite LA-2/MIBK and finally Cr(VI) was determined in the organic extract and Cr(III) in the aqueous phase using GFAAS. The method was evaluated by analysis of the certified reference material, CRM 544, and good accuracy was obtained. The limit of detection for Cr(VI) and Cr(tot)/Cr(III) was found to be 0.30 and 0.08 µg L⁻¹, respectively, and a precision expressed as relative standard deviation of better than 11% was achieved for nine replicates. A number of water samples from the Tinishu Akaki River, Ethiopia, and wastewater samples from a chemical plant in Germany, were analysed. In addition to the GFAAS method, Cr(tot) was also determined using ICP-MS (in CRM 544, lyophilized water, and Tinishu Akaki River water samples) and Cr(tot) and Cr(VI) using UV-VIS spectrophotometry (in CRM 544 and industrial wastewater samples). Good agreement between the different methods was found.     

Current mass spectrometry strategies for selenium speciation in dietary sources of high-selenium

This document reviews the most relevant mass spectrometry approaches to selenium (Se) speciation in high-Se food supplements in terms of qualitative and quantitative Se speciation and Se-containing species identification, with special reference to high-Se yeast, garlic, onions and Brazil nuts. Important topics such as complexity of Se speciation in these materials and the importance of combining Se-specific detection and molecule-specific determination of the particular species of this element in parallel with chromatography, to understand their nutritional role and cancer preventive properties are critically discussed throughout. The versatility and potential of mass spectrometric detection in this field are clearly demonstrated. Although great advances have been achieved, further developments are required, especially if speciatedcertified reference materials (CRMs) are to be produced for validation of measurements of target Se-containing species in Se-food supplements.     

The Chemical Speciation and Behavior of Mercury and Selenium in the Insoluble Fraction of Striped Dolphin Liver

Most of the mercury and selenium exist in the insoluble fraction of dolphin liver. After the insoluble fraction was digested by alkaline protease in the presence of 1% SDS, approximately 50% of Hg and Se consisted in the supernatant and the others in the residue. Gel filtration chromatography of the hydrolysate showed that 96% of Hg and 87% of Se were combined with the high molecular weight proteins stably, which cannot be substituted by the complex reagents.Mercury and selenium in the residue were confirmed as HgSe crystal.     

Combination of three analytical techniques for speciation of Al in environmental samples

An analytical scheme is proposed which combines three speciation techniques for determination of particular Al species in soil extracts and percolating waters. A cation-exchange fast protein liquid chromatography — inductively coupled plasma atomic emission spectrometry (FPLC-ICP-AES) procedure, a microcolumn chelating ion-exchange chromatography- atomic absorption spectrometry (MCC-ETAAS) technique and the 8-hydroxyquinoline spectrophotometric method (8HQ-spectrophotometry) were employed. The FPLC-ICP-AES procedure offers determination of Al³⁺ (retention time 4.5 min) and Al(OH)²⁺ species (retention time 4.0 min) which are separated from Al(OH)⁺ ₂ (retention time 1.5min). AlF²⁺ coelutes with Al(OH)²⁺ species, while Al(SO₄)⁺, AlF⁺ ₂ and negatively charged Al organic complexes coelute with Al(OH)⁺ ₂ species. The MCC-ETAAS technique enables determination of the sum of positively charged monomeric aqua- and hydroxy-Al species plus sulphate- and fluoro-Al complexes. Employing the 8HQ-spectrophotometry the sum of positively charged monomeric aqua- and hydroxy-Al species plus sulphato- and most of the labile organic Al species are determined. The sensitivities of these selected techniques were adequate for speciation of Al in the samples analyzed. On the basis of the specific selectivity of a particular technique various groups of Al species may be determined. Thus, the comparison of analytical data from complementary procedures provides more comprehensive information on Al species present in soil extracts and percolating waters.     

Mercury species immobilized on sulphydryl cotton: A new candidate reference material for mercury speciation

A batch of sulphydryl cotton microcolumns was prepared and charged with a mixed Hg standard solution (methyl-, ethyl- and inorganic Hg, 10 g l^–1 as Hg, 3 ml) and stored at 4 °C in a light-tight box. At regular time intervals over a 4 month period microcolumns were removed and Hg species were quantified by gas chromatography microwave-induced plasma atomic emission spectrometry (after elution, extraction and derivatization steps). It was found that analyte recoveries for methyl- and inorganic Hg were quantitative over the 4 month period while ethyl-Hg species appeared to be stable for up to 2 months.