Trends in speciation analysis of vanadium in environmental samples and biological fluids--a review

High-throughput Sequencing Analysis of the Effects of Vanadium on Bacterial Community Structure in Purple Soil

Vanadium (V) contamination in soil has received extensive attention due to its high toxicity. The change of mobility and bioavailability of soil V and the effects of V on the soil microbial community were studied under conditions of different V(V) spiking concentrations (0, 100, 250, and 500 mg kg-1) and aging time (1, 7, 14, 30, 45, and 60 d). The results showed that soil V mainly presented as V(IV) of all treatments throughout the aging process. At high levels of V(V) loading (250 and 500 mg kg-1), soil V(V) showed a downward trend, while bioavailable V did not change significantly within 60 d's aging. The analysis of soil bacterial community showed that Proteobacteria was the most abundant phylum in all soils, and the dominant genera Sphingomonas and Lysobacter can well adapt to high concentration V. These microorganisms exhibited great potential for bioremediation of V-contaminated soils.

Synthesis of a novel magnetic nanomaterial for the development of a multielemental speciation method of lead, mercury, and vanadium via HPLC-ICP MS

A new magnetic functionalized material based on graphene oxide magnetic nanoparticles named by us, M@GO-TS, was designed and characterized in order to develop a magnetic solid-phase extraction method (MSPE) to enrich inorganic and organic species of lead, mercury, and vanadium. A flow injection (FI) system was used to preconcentrate the metallic and organometallic species simultaneously, while the ultra-trace separation and determination of the selected species were achieved by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP MS). Therefore, preconcentration and separation/determination processes were automated and conducted separately. To the best of our knowledge, this is the first method combining an online MSPE and HPLC-ICP MS for multielemental speciation. Under the optimized conditions, the enrichment factor obtained for Pb^II, trimethyllead (TML), Hg^II, methylmercury (MetHg), and V^V was 27. The calculated LOD for all studied species were as follows: 5 ng L^-1, 20 ng L^-1, 2 ng L^-1, 10 ng L^-1, and 0.4 ng L^-1, respectively. The RSD values calculated with a solution containing 0.5 μg L^-1 of all species were between 2.5 and 4.5%. The developed method was validated by analyzing Certified Reference Materials TMDA 64.3 for total concentration and also by recovery analysis of the species in human urine from volunteers and a seawater sample collected in Málaga. The t statistical test showed no significant differences between the certified and found values for TMDA 64.3. All the recoveries obtained from spiked human urine and seawater samples were close to 100%. All samples were analyzed using external calibration. The developed method is sensitive and promising for routine monitoring of the selected species in environmental waters and biological samples.

Risk assessment and microbial community structure in agricultural soils contaminated by vanadium from stone coal mining

High health risks of vanadium (V) released by the mining of vanadium titanomagnetite (VTM) have been widely recognized, but little is known about the risks and microbial community responses of V pollution as a consequence of the stone coal mining (SCM), another important resource for V mining. In this study, the topsoils and the profile soils were collected from the agricultural soils around a typical SCM in Hunan Province, China, with the investigation of ecological, health risks and microbial community structures. The results showed that ∼97.6% of sampling sites had levels of total V exceeding the Chinese National standard (i.e., 130 mg/kg), and up to 41.1% of V speciation in the topsoils was pentavalent vanadium (V(V)). Meanwhile, the proportions of HQ > 1 and 0.6-1 in the topsoils were ∼8.3% and ∼31.0% respectively, indicating that V might pose a non-carcinogenic risk to children. In addition, the microbial community varied between the topsoils and the profile soils. Both sulfur-oxidizing bacteria (e.g. Thiobacillus, MND1, Ignavibacterium) and sulfate-reducing bacteria (e.g. Desulfatiglans, GOUTB8, GOUTA6) might have been involved in V(V) reductive detoxification. This study helps better understand the pollution and associated risks of V in the soils of SCM and provides a potential strategy for bioremediation of the V-contaminated environment.

Vanadium: A Review of Different Extraction Methods to Evaluate Bioavailability and Speciation

The excessive input of heavy metals such as vanadium (V) into the environment has been one of the consequences of global industrial development. Excessive exposure to V can pose a potential threat to ecological safety and human health. Due to the heterogeneous composition and reactivity of the various elements in soils and sediments, quantitative analysis of the chemical speciation of V in different environmental samples is very complicated. The analysis of V chemical speciation can further reveal the bioavailability of V and accurately quantify its ecotoxicity. This is essential for assessing for exposure and for controlling ecological risks of V. Although the current investigation technologies for the chemical speciation of V have grown rapidly, the lack of comprehensive comparisons and systematic analyses of these types of technologies impedes a more comprehensive understanding of ecosystem safety and human health risks. In this review, we studied the chemical and physical extraction methods for V from multiple perspectives, such as technological, principle-based, and efficiency-based, and their application to the evaluation of V bioavailability. By sorting out the advantages and disadvantages of the current technologies, the future demand for the in situ detection of trace heavy metals such as V can be met and the accuracy of heavy metal bioavailability prediction can be improved, which will be conducive to development in the fields of environmental protection policy and risk management.

Redox Speciation of Vanadium in Estuarine Waters Using Improved Methodology Based on Anion Exchange Chromatography Coupled to HR ICP-MS System

An improved methodology was developed for V redox speciation in estuarine waters using a hyphenated technique consisting of ion chromatograph (IC) with an anion exchange column and a high-resolution inductively coupled plasma mass spectrometer (HR ICP-MS). This approach enables the direct determination of V(V), whereas reduced species (mainly V(IV)) are calculated by subtracting V(V) concentrations from the measured total V concentration. Based on the “on-column” V(V) chelation mechanism by EDTA, with the eluent composed of 40 mmol L⁻¹ ammonium bicarbonate, 40 mmol L⁻¹ ammonium sulphate, 8 mmol L⁻¹ ethylenediaminetetraacetic acid and 3% acetonitrile, the method was successfully used for analyses of V redox speciation in samples taken in the vertical salinity gradient of the highly stratified Krka River estuary. Due to the matrix effects causing different sensitivities, a standard addition method was used for V(V) quantification purposes. The limit of detection (LOD) was also found to be matrix related: 101.68 ng L⁻¹ in the seawater and 30.56 µg L⁻¹ in the freshwater. Performed stability tests showed that V redox speciation is preserved at least 7 days in un-treated samples, possibly due to the stabilization of V-reduced species with natural organic matter (NOM). The dominant V form in the analysed samples was V(V) with the reduced V(IV) accounting for up to 26% of the total dissolved pool. The concentration of V(IV) was found to correlate negatively with the oxygen concentration. Significant removal of dissolved V was detected in oxygen depleted zones possibly related to the particle scavenging.

Vanadium: environmental hazard or environmental opportunity? A perspective on some key research needs

Vanadium remains an important microalloying element in the metallurgical industry and has more recently become important in energy storage. Such applications provide important opportunities in carbon reduction initiatives. They must be exploited safely and therefore understanding the toxicological profile of vanadium and its compounds, and ensuring ongoing regulatory efforts are appropriate is vital. This perspective details some of the technical challenges and common misconceptions in vanadium chemistry and toxicology and outlines knowledge gaps and areas of research that the authors believe must be addressed to achieve full benefit within a scientifically sound regulatory framework.

Redox chemistry of vanadium in soils and sediments: Interactions with colloidal materials, mobilization, speciation, and relevant environmental implications- A review

Vanadium (V), although serving as an important component of industrial activities, has bioinorganic implications to pose highly toxic hazards to humans and animals. Soils and sediments throughout the world exhibit wide ranges of vanadium concentrations. Although vanadium toxicity varies between different species, it is mainly controlled by soil redox potential (E_H). Nonetheless, knowledge of the redox geochemistry of vanadium lags in comparison to what is known about other potentially toxic elements (PTEs). In particular, the redox-induced speciation and mobilization of vanadium in soils and sediments and the associated risks to the environment have not been reviewed to date. Therefore, this review aims to address 1) the content and geochemical fate of vanadium in soils and sediments, 2) its redox-induced release dynamics, 3) redox-mediated chemical reactions between vanadium and soil organic and inorganic colloidal materials in soil solution, 4) its speciation in soil solution and soil-sediments, and 5) the use of advanced geochemical and spectroscopic techniques to investigate these complex systems. Vanadium (+5) is the most mobile and toxic form of its species while being the thermodynamically stable valence state in oxic environments, while vanadium (+3) might be expected to be predominant under euxinic (anoxic and sulfidic) conditions. Vanadium can react variably in response to changing soil E_H: under anoxic conditions, the mobilization of vanadium can decrease because vanadium (+5) can be reduced to relatively less soluble vanadium (+4) via inorganic reactions such as with H₂S and organic matter and by metal-reducing microorganisms. On the other hand, dissolved concentrations of vanadium can increase at low E_H in many soils to reveal a similar pattern to that of Fe, which may be due to the reductive dissolution of Fe(hydr)oxides and the release of the associated vanadium. Those differences in vanadium release dynamics might occur as a result of the direct impact of E_H on vanadium speciation in soil solution and soil sediments, and/or because of the E_H-dependent changes in soil pH, chemistry of (Fe)(hydr)oxides, and complexation with soil organic carbon. Release dynamics of vanadium in soils may also be affected positively by soil pH and the release of aromatic organic compounds. X-ray absorption spectroscopy (XAS) is a powerful tool to investigate the speciation of vanadium present in soil. X-ray absorption near edge structure (XANES) is often used to constrain the average valence state of vanadium in soils and sediments, and in limited cases extended X-ray absorption fine structure (EXAFS) analysis has been used to determine the average molecular coordination environment of vanadium in soil components. In conclusion, this review presents the state of the art about the redox geochemistry of vanadium and thus contributes to a better understanding of the speciation, potential mobilization, and environmental hazards of vanadium in the near-surface environment of uplands, wetlands, and agricultural ecosystems as affected by various colloidal particles. Further research is needed to elucidate the geochemistry and speciation of vanadium in the dissolved, colloidal, and soil sediments phases, including the determination of factors that control the redox geochemistry of vanadium.

An extraction-chromogenic system for vanadium(IV,V) based on 2,3-dihydroxynaphtahlene

A liquid-liquid extraction-chromogenic system for vanadium(IV, V) containing 2,3-dihydroxynaphtahlene (DN), 2,3,5-triphenyl-2H-tetrazolium chloride (TTC), water and chloroform was studied in detail. When the vanadium is in the oxidation state of IV, the extracted species are aggregates containing three 1:2:1 (V:DN:TTC) ion-pair units composed of triphenyltetrazolium cations (TT+) and chelate anions {[VIVO(DN)(DNH)]− (I) and/or [VIV(OH)(DN)2]− (II)}. When the initial oxidation state of vanadium is V and the DN concentration is high, vanadium(V) is reduced by DN to a lower oxidation state, V(IV). However, at low DN concentration, vanadium(V) can enter the organic phase as a part of an ion-pair consisting of TT+ and [VVO2(DN)]− (III). The ground-state equilibrium geometries of the anions I, II, and III were optimized by quantum chemical calculations using BLYP/6-31++G⋆. The following characteristics were determined under the optimum conditions for VIV extraction: absorption maximum λmax = 333 nm, molar absorptivity ε333= 2.1x104 dm3 mol−1 cm−1, Sandell’s sensitivity SS = 2.4 ng cm−2, and fraction extracted E = 98%. The conditional extraction constant was calculated by two independent methods. The calibration graph was linear in the range 0.1-3.1 μg cm−3 (R2=0.9994) and the limit of detection was 0.03 μg cm−3.

Effectiveness of vegetation buffers surrounding playa wetlands at contaminant and sediment amelioration

Playa wetlands, the dominant hydrological feature of the semi-arid U.S. High Plains providing critical ecosystem services, are being lost and degraded due to anthropogenic alterations of the short-grass prairie landscape. The primary process contributing to the loss of playas is filling of the wetland through accumulation of soil eroded and transported by precipitation from surrounding cultivated watersheds. We evaluated effectiveness of vegetative buffers surrounding playas in removing metals, nutrients, and dissolved/suspended sediments from precipitation runoff. Storm water runoff was collected at 10-m intervals in three buffer types (native grass, fallow cropland, and Conservation Reserve Program). Buffer type differed in plant composition, but not in maximum percent removal of contaminants. Within the initial 60 m from a cultivated field, vegetation buffers of all types removed >50% of all measured contaminants, including 83% of total suspended solids (TSS) and 58% of total dissolved solids (TDS). Buffers removed an average of 70% of P and 78% of N to reduce nutrients entering the playa. Mean maximum percent removal for metals ranged from 56% of Na to 87% of Cr. Maximum removal was typically at 50 m of buffer width. Measures of TSS were correlated with all measures of metals and nutrients except for N, which was correlated with TDS. Any buffer type with >80% vegetation cover and 30-60 m in width would maximize contaminant removal from precipitation runoff while ensuring that playas would continue to function hydrologically to provide ecosystem services. Watershed management to minimize erosion and creations of vegetation buffers could be economical and effective conservation tools for playa wetlands.

Vanadium, recent advancements and research prospects: A review

Metal pollution is an important issue worldwide, with various documented cases of metal toxicity in mining areas, industries, coal power plants and agriculture sector. Heavy metal polluted soils pose severe problems to plants, water resources, environment and nutrition. Among all non-essential metals, vanadium (V) is becoming a serious matter of discussion for the scientists who deals with heavy metals. Due to its mobility from soil to plants, it causes adverse effects to human beings. This review article illustrates briefly about V, its role and shows the progress about V research so far done globally in the light of the previous work which may assist in inter-disciplinary studies to evaluate the ecological importance of V toxicity.

Accumulation and speciation of vanadium in Lycium seedling

Lycium seedling was subjected to varying doses of V for 40-45 days to examine the effects on uptake, accumulation, and speciation of V in Lycium seedling by differential centrifugation and enzymolysis. V concentrations in Lycium seedling organs were in sequence as follows: root>leaf>stem. V uptake into stem and leaf were primarily combined with acid-soluble polar compounds, polysaccharide, and immobile materials on the cell walls. There were different speciations of V in root with different V stress levels. Enzymolysis results suggest that about 60% of the V in Lycium seedling root was combined with pectin and cellulose. It is the antidotal effect of pectin and cellulose in the cell wall that reduced the V damage to Lycium seedling.

Release of vanadium from oxidized sediments: insights from different extraction and leaching procedures

Although the attention for vanadium (V) as a potentially harmful element is growing and some countries adopted threshold values for V in soils, sediments, groundwater, or surface water, V is generally of little importance in environmental legislation and the knowledge about the behavior of V in the environment is still limited. In the present study, the release of V from oxidized sediments, sediment-derived soils, and certified reference materials was investigated by means of several types of leaching tests and extractions that are frequently used for soil and sediment characterization. The pHstat leaching tests and single and sequential extractions applied in this study show that V generally displays a very limited actual and potential mobility in sediment. "Mobile" V concentrations, as estimated by the amount of V released by a single extraction with CaCl2 0.01 mol L(-1), were low, even in the most contaminated sediment samples. Only under strongly acidifying conditions (pH 2), such as in the case of ingestion of soil or sediment or in accidental spills, a substantial release of V can be expected.

Chemical, biochemical, and biological behaviors of vanadate and its oligomers

Vanadate is widely used as an inhibitor of protein tyrosine phosphatases (PTPase) and is routinely applied in cell lysis buffers or immunoprecipitations of phosphotyrosyl proteins. Additionally, vanadate has been extensively studied for its antidiabetic and anticancer effects. In most studies, orthovanadate or metavanadate was used as the starting compound, whereas these "vanadate" solutions may contain more or less oligomerized species. Whether and how different species of vanadium compounds formed in the biological media exert specific biological effect is still a mystery. In the present commentary, we focus on the chemical, biochemical, and biological behaviors of vanadate. On the basis of species formation of vanadate in chemical and biological systems, we compared the biological effects and working mechanism of monovanadate with that of its oligomers, especially the decamer. We propose that different oligomers may exert a specific biological effect, which depends on their structures and the context of the cell types, by different modes of action.

Uptake and speciation of vanadium in the benthic invertebrate Hyalella azteca

Vanadium has the potential to leach into the environment from petroleum coke, an oil sands byproduct. To determine uptake of vanadium species in the biota, we exposed the benthic invertebrate Hyalella azteca with increasing concentrations of two different vanadium species, V(IV) and V(V), for seven days. The concentrations of vanadium in the H. azteca tissue increased with the concentration of vanadium in the exposure water. Speciation analysis revealed that V(IV) in the exposure water was oxidized to V(V) between renewal periods, and therefore the animals were mostly exposed to V(V). Speciation analysis of the H. azteca tissue showed the presence of V(V), V(IV), and an unidentified vanadium species. These results indicate the uptake and metabolism of vanadium by H. azteca. Because H. azteca are widely distributed in freshwater systems and are an important food supply for many fish, determining the uptake and metabolism of vanadium allows for a better understanding of the potential environmental effects on invertebrates.

Rapid speciation and determination of vanadium compounds using ion-pair reversed-phase ultra-high-performance liquid chromatography inductively coupled plasma-sector field mass spectrometry

Environmental vanadium contamination is a potential concern to public health, as evidenced by its place on the U.S. Environmental Protection Agency Drinking Water Contaminant Candidate List as a priority contaminant. Vanadium toxicity varies significantly between different oxidation states; therefore, it is crucial to be able to monitor the speciation of vanadium in environmental samples. In this study, a novel method is described that utilizes ion-pair reversed-phase ultra-high-performance liquid chromatography with inductively coupled plasma-sector field mass spectrometry (IP-RP-UHPLC-ICP-SFMS) to separate vanadyl and vanadate ions and resolve a major polyatomic spectral interference ((35)Cl(16)O(+)) in less than a minute. Detection limits were obtained in the low ngL(-1) (part per trillion) range with linear calibrations across several orders of magnitude (50ngL(-1)-100μgL(-1)). The mechanism of chromatographic retention was elucidated through investigation of the role of ethylenediaminetetraacetic acid, tetrabutylammonium ion and pH on elution. The optimized method was then applied to the speciation of vanadium in local lake water samples.

Chemical speciation of vanadium in particulate matter emitted from diesel vehicles and urban atmospheric aerosols

We report on the development and application of an integrated set of analytical tools that enable accurate measurement of total, extractable, and, importantly, the oxidation state of vanadium in sub-milligram masses of environmental aerosols and solids. Through rigorous control of blanks, application of magnetic-sector-ICPMS, and miniaturization of the extraction/separation methods we have substantially improved upon published quantification limits. The study focused on the application of these methods to particulate matter (PM) emissions from diesel vehicles, both in baseline configuration without after-treatment and also equipped with advanced PM and NO(x) emission controls. Particle size-resolved vanadium speciation data were obtained from dynamometer samples containing total vanadium pools of only 0.2-2 ng and provide some of the first measurements of the oxidation state of vanadium in diesel vehicle PM emissions. The emission rates and the measured fraction of V(V) in PM from diesel engines running without exhaust after-treatment were both low (2-3 ng/mile and 13-16%, respectively). The V(IV) species was measured as the dominant vanadium species in diesel PM emissions. A significantly greater fraction of V(V) (76%) was measured in PM from the engine fitted with a prototype vanadium-based selective catalytic reductors (V-SCR) retrofit. The emission rate of V(V) determined for the V-SCR equipped vehicle (103 ng/mile) was 40-fold greater than that from the baseline vehicle. A clear contrast between the PM size-distributions of V(V) and V(IV) emissions was apparent, with the V(V) distribution characterized by a major single mode in the ultrafine (<0.25 μm) size range and the V(IV) size distribution either flat or with a small maxima in the accumulation mode (0.5-2 μm). The V(V) content of the V-SCR PM (6.6 μg/g) was 400-fold greater than that in PM from baseline (0.016 μg/g) vehicles, and among the highest of all environmental samples examined. Synchrotron based V 1s XANES spectroscopy of vanadium-containing fine-particle PM from the V-SCR identified V(2)O(5) as the dominant vanadium species.

Bioavailability of vanadium extracted by EDTA, HCl, HOAC, and NaNO3 in topsoil in the Panzhihua urban park, located in southwest China

Bioavailable vanadium was evaluated on the basis of soil vanadium single-extraction with ethylenediaminetetraacetic acid (EDTA), hydrochloric acid (HCl), acetic acid (HOAc), and sodium nitrate (NaNO(3)) in Panzhihua urban park. The soil vanadium concentration extracted by HOAc was 0.01-2.07 mg kg(-1), by EDTA 0.28-7.03 mg kg(-1), by NaNO(3) 0.07-0.53 mg kg(-1), and by HCl 0.19-1.36 mg kg(-1). The bioavailable vanadium (bioavailable fraction) obtained with HOAc was 0.01-1.33%, with EDTA 0.27-4.09%, with NaNO(3) 0.13-0.72%, and with HCl 0.06-0.28%. In addition, the impact of soil properties, soil nutrients, and soil enzyme activities on bioavailability of vanadium is discussed in this study. Based on the characteristics of bioavailable vanadium in the soil, ecological and health risks should have been given more attention in the studied area.

Hazardous impact and translocation of vanadium (V) species from soil to different vegetables and grasses grown in the vicinity of thermal power plant

The distribution of vanadium (V) species in soil (test soil), vegetables and grasses, collected from the vicinity of a thermal power plant has been studied. For comparison purpose soil (control soil), same vegetable and grass samples were collected from agricultural land devoid of any industrial area. A simple and efficient ultrasonic assisted extraction method has been developed for the extraction of V(5+) species from soil, vegetable and grass samples using Na(2)CO(3) in the range of 0.1-0.5 mol/L. For comparison purpose same sub samples were also extracted by conventional heating method. The total and V species were determined by electrothermal atomic absorption spectrometry using different modifiers. The validity of V(5+) and V(4+) determination had been confirmed by the spike recovery and total amount of V by the analysis of CRM 1570 (spinach leave) and sub samples of agricultural soil. The concentration of total V was found in the range of 90-215 and 11.4-42.3 μg/g in test and control soil samples, respectively. The contents of V(5+) and total V in vegetables and grasses grown around the thermal power plant were found in the range of 2.9-5.25 and 8.74-14.9 μg/g, respectively, which were significantly higher than those values obtained from vegetables and fodders grown in non exposed agricultural site (P<0.01). Statistical evaluations indicate that the sum of concentrations of V(5+) and V(4+) species was not significantly different from total concentration of V in same sub samples of vegetable, grass and soil of both origins, at 95% level of confidence.

Environmental vanadium distribution, mobility and bioaccumulation in different land-use districts in Panzhihua Region, SW China

In order to characterize environmental vanadium distribution, mobility, and bioaccumulation, a total of 55 soil samples and 36 plant samples were collected in four typical land-use districts in Panzhihua region, Southwestern China. Soil samples were analyzed with the modified Community Bureau of Reference (BCR) sequential extraction procedure, and the content of vanadium in soil and plant was determined by ICP-AES. The total content of vanadium was 208.1-938.4 mg kg(-1) in smelting area, 111.6-591.2 mg kg(-1) in mining area, 94.0-183.6 mg kg(-1) in urban park, and 71.7-227.2 mg kg(-1) in agricultural area, respectively, while the bio-available content of vanadium was characterized that the polluted areas (mining area 18.8-83.6 mg kg(-1), smelting area 41.7-132.1 mg kg(-1)) and the unpolluted area (agricultural area 9.8-26.4 mg kg(-1), urban park 9.9-25.2 mg kg(-1)). In addition, the contamination degree of vanadium in soil was smelting area > mining area > agricultural area ≈ urban park. Moreover, the fraction of vanadium in each sequential extraction characterized that residual fraction > oxidizable fraction > reducible fraction > acid soluble fraction. The bioaccumulation of vanadium from soil to plant was weak to intermediate absorption. Therefore, some countermeasures such as soil monitoring and remediation should be to take in the sooner future, especially in mining and smelting area.

Recent applications of carbon-based nanomaterials in analytical chemistry: critical review

The objective of this review is to provide a broad overview of the advantages and limitations of carbon-based nanomaterials with respect to analytical chemistry. Aiming to illustrate the impact of nanomaterials on the development of novel analytical applications, developments reported in the 2005-2010 period have been included and divided into sample preparation, separation, and detection. Within each section, fullerenes, carbon nanotubes, graphene, and composite materials will be addressed specifically. Although only briefly discussed, included is a section highlighting nanomaterials with interesting catalytic properties that can be used in the design of future devices for analytical chemistry.

Analysis of soil reference materials for vanadium(+5) species by electrothermal atomic absorption spectrometry

Solid Certified Reference Materials (CRMs) with known vanadium(+5) content are currently not commercially available. Because of this, vanadium species have been determined in solid CRMs of soil, viz. CRM023-50, CRM024-50, CRM049-50, SQC001 and SQC0012. These CRMs are certified with only total vanadium content. Vanadium(+5) was extracted from soil reference materials with 0.1M Na(2)CO(3). The quantification of V(+5) was carried out by electrothermal atomic absorption spectrometry (ET-AAS). The concentration of V(+5) in the analyzed CRMs was found to be ranging between 3.60 and 86.0 microg g(-1). It was also found that SQC001 contains approximately 88% of vanadium as V(+5) species. Statistical evaluation of the results of the two methods by paired t-test was in good agreement at 95% level of confidence.

On-line separation/preconcentration of V(IV)/V(V) in environmental water samples with CTAB-modified alkyl silica microcolumn and their determination by inductively coupled plasma-optical emission spectrometry

A simple and selective method of flow injection microcolumn separation/preconcentration on-line coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed for the speciation of V(V)/(IV). Various factors affecting the separation/preconcentration of V(IV) and V(V) by conical microcolumn packed with cetyltrimethylammonium bromide (CTAB)-modified alkyl silica have been systematically investigated. It is found that V(V) was quantitatively retained by the microcolumn at pH 2.0-7.0, while V(IV) was not retained by the microcolumn at pH 2.0-3.5 but quantitatively retained at pH 5.0-7.0. The two vanadium species adsorbed by the modified adsorbent were quantitatively desorbed by 0.10 mL of 1.0 mol L(-1) HNO(3). Therefore, V(V) and total vanadium could be determined by CTAB-modified alkyl silica packed microcolumn separation/preconcentration and on-line ICP-OES detection after adjusting sample solution to pH 2.5 and 6.0, respectively, and the assay of V(IV) was realized by subtracting V(V) from total V. The detection of limit (LOD) for V(V) was 0.03 microg L(-1) with an enrichment factor of 27.9 for a 3.0 mL sample consumption. The relative standard deviations (RSDs) (C(V(V))=C(V(IV))=5.0 microg L(-1), n=9) were 4.3% and 4.0% for V(V) and total V, respectively. The developed method was validated by the determination of V(IV) and V(V) in environmental water samples.

Ternary complexes of vanadium(IV) with 4-(2-pyridylazo)-resorcinol (PAR) and ditetrazolium chlorides (DTC)

Complex formation and liquid-liquid extraction have been studied for ternary complexes of vanadium(IV) with 4-(2-pyridylazo)-resorcinol (PAR) and ditetrazolium chlorides (DTC) in a water-chloroform medium. The specific ditetrazolium compounds investigated were i) 3,3′-(4,4′-biphenylene)-bis(2,5-diphenyl-2H-tetrazolium) chloride (Neotetrazolium chloride, NTC); ii) 3,3′-(3,3′-dimetoxy-4,4′-biphenylene)-bis(2,5-diphenyl-2H-tetrazolium) chloride (Blue Tetrazolium chloride, BTC); and iii) 3,3′-(3,3′-dimetoxy-4,4′-biphenylene)-bis[2-(4-nitrophenyl)-5-phenyl-2H-tetrazolium] chloride (Nitro Blue Tetrazolium chloride, NBT). Molar absorptivity coefficients and the composition of the complexes have been calculated. Association constants (β) have also been obtained for the interactions between the vanadium(IV) — PAR anionic chelates [VO(PAR)2]2− (I) and [VO(OH)2(PAR)2]4− (II), and ditetrazolium cations (DT2+). Some special features of NBT as an extraction-spectrophotometric reagent for vanadium(IV) have been discussed. Unlike NTC and BTC which form complexes with both I and II, NBT associates only with II. The pH interval for complete extraction of (NBT2+)2[VO(OH)2(PAR)2] is broader and allows work at lower pH values the other ion-associates of V(IV,V)-PAR that were studied. NBT is -therefore the appropriate reagent both for direct V(IV) determination and for V(IV)/V(V) separation. Some additional characteristics for the V(IV)-PAR-NBT-water-chloroform system have been determined: extraction constant, distribution constant, recovery factor, limit of detection and limit of quantification. Beer’s law is valid up to 1.4 μg mL−1 vanadium(IV) with molar absorptivity coefficient of 3.55×104 L mol−1 cm−1 at λmax=559 nm.

A sensitive method for determining total vanadium in water samples using colorimetric-solid-phase extraction-fiber optic reflectance spectroscopy

A selective colorimetric-solid-phase extraction (C-SPE) method for the determination of total vanadium in water samples was developed. This method introduced a new variation of C-SPE. The colour reaction is based on the reaction of vanadium(V) ternary complex formed with 1-(2-Pyridylazo)-2-naphtol (PAN) in the presence hydrogen peroxide (H(2)O(2)). In this technique, the target analytes in samples are extracted onto solid matrix loaded with a colorimetric reagent and then quantified directly on the adsorbent surface by using a miniature fiber optic reflectance spectrometer. The measurements were carried out at a wavelength of 589.4 nm since it yielded the largest divergence different in reflectance spectra before and after reaction with the vanadium. The overall time required for the C-SPE procedure was approximately 20 min. The amount of concentrated V is then determined in a few seconds by using miniature reflectance spectrometer. At the optimal conditions, a calibration curve was constructed, revealing a linear range of 0.05-0.52 mg L(-1) and a detection limit as low as 0.01 mg L(-1) while the RSD lower than 2.8%. In order to verify the accuracy of the method, a certified reference water samples (TMDA) were analysed and the results obtained were in good agreement with the certified values. The proposed method was applied to the determination of vanadium in tap water, seawater samples with a recovery for the spiked samples in the range of 98-102%.