Ethylenediaminetetraacetato-monoperoxo complexes of vanadium(V)

Summary The monoperoxo complexes, M₂[VO(HEDTA)(O₂)]· 4H₂O, where M is K⁺ or NH ₄ ⁺ and H₄EDTA is ethylene-diaminetetraacetic acid, were prepared and characterized by Raman and i.r. spectra in the solid state and in aqueous solution. The single crystal X-ray study revealed a pentagonal bipyramidal anion structure with a tetradentate HEDTA(3—) ligand. The decomposition of complexes in aqueous solution to blue vanadium(IV) complexes as end products proceeds via a nonperoxo complex of vanadium.     

Speciation analysis of inorganic vanadium (V(IV)/V(V)) by graphite furnace atomic absorption spectrometry following ion-exchange separation

A sensitive and simple method of ion-exchange resin separation and graphite-furnace atomic absorption spectrometry (GFAAS) detection was proposed for the determination of inorganic vanadium species. Methylene Blue (MB) was used as a chelating agent of V(V) for ion-exchange separation. The complex of V(V) and MB could be trapped by ion-exchange resin at pH 3.0 and eluted by 1.0?mol?L^?1 NaOH. The vanadium species was determined subsequently by GFAAS. The concentration of V(IV) was calculated by subtracting the V(V) concentration from the total concentration of vanadium. Under the optimized experimental conditions, the detection limit of V(V) is 0.48?µg?L^?1 with RSD of 2.6% (n?=?5, c?=?2.0?µg?L^?1). In order to verify the accuracy of the method, a certified reference soil sample was analyzed, and the results obtained were in good agreement with the certified values. The range of recovery for V(IV) and V(V) was 97.8–99.3% and 101.7–103.6%, respectively. The proposed method was applied to the speciation analysis of vanadium in lake-water samples.     

Monitoring of V(IV) and V(V) in Etnean drinking-water distribution systems by solid phase extraction and electrothermal atomic absorption spectrometry

Monitoring activities carried out since 1994 showed the presence of significant levels of vanadium in drinking waters delivered in a lot of Etnean towns. The highest vanadium concentration was found in ground waters collected in the drainage gallery Ciapparazzo located on the Northwestern flank of Mt. Etna in Bronte's area (Catania, Italy). This drainage gallery, with a flow rate of near 500 l s^− 1, is an important water source for several towns of the Etnean province. On account of different toxicological behaviours of V(IV) and V(V), which are the only possible oxidation states in aqueous media, a research project was set up to evaluate the ratio between their concentrations before and after disinfection treatments (chlorination or UV irradiation). Data were acquired in the most representative sites of the drainage gallery and the distribution network to evaluate the effect of residence times and disinfection treatments on possible species interconversion. The average total concentration of vanadium was 165 μg l^− 1. Speciation analyses performed by solid phase extraction of both species followed by furnace atomic absorption spectrometric determination of V(IV) eluates revealed that the latter was the predominant species (90-100%) in untreated waters. Moreover, among the two disinfecting treatments applied by the water supplier, only sodium hypochlorite altered the species ratio and determined an instant increase of near 20% in V(V) relative concentration. No significant effect was observed as residence time varied in the drainage gallery or in the distribution systems. Other physico-chemical and chemical parameters (i.e. pH, E_H, water temperature, electrical conductance, dissolved oxygen as well as major and minor inorganic cations and anions) were determined in the collected water samples to evaluate if they are proper or not for interconversion of the two V species. Redox potential of the water was also correlated to the percentage of V(IV).     

Speciation analysis of vanadium in natural water samples by electrothermal vaporization inductively coupled plasma optical emission spectrometry after separation/preconcentration with thenoyltrifluoroacetone immobilized on microcrystalline naphthalene

A sensitive and simple method for low temperature electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICP-OES) determination of V(IV) and V(V) after separation/preconcentration by a micro-column packed with immobilized thenoyltrifluoroacetone (TTA) on microcrystalline naphthalene has been developed. Thenoyltrifluoroacetone was used as both a chelating agent for micro-column separation/preconcentration and a chemical modifier for ETV-ICP-OES determination of vanadium. Both vanadium species could be trapped by micro-column at pH 4.0, and the vanadate (VO₂⁺) ion could be collected selectively at pH 2.4. Solid material loaded with analyte in the micro-column was dissolved with 100 μL of acetone containing 2.0 mmol L⁻¹ TTA and the vanadium was determined subsequently by ETV-ICP-OES. The concentration of vanadyl (VO²⁺) ion was calculated by subtracting the vanadate concentration from the total concentration of vanadium. Under the optimized experimental conditions, the detection limit (3σ) for the preconcentration of 5 mL of aqueous solution is 0.068 μg L⁻¹ for both species and the relative standard deviations were 4.3% for vanadium(V) and 4.8% for vanadium(IV) (c=10 μg L⁻¹, n=7), respectively. The method was applied successfully to the determination of vanadium(IV) and vanadium(V) in natural water samples.     

Determination of Vanadium(IV) and Vanadium(V) in Benfield Samples by IEC with Conductivity Detection

In this study, the determination of vanadium valence state, V(IV) and V(V) has been achieved using ion-exchange chromatography with conductivity detector. In this method, V(IV) was determined as V(IV)-EDTA complex and V(V) as vanadate ion. Determination of V(IV) was successfully done using 3 mM carbonate/bicarbonate/EDTA at pH 8.6 as the eluent. The additive, EDTA in the mobile phase did not seem to interfere with the V(IV) analysis. The detection of V(V) was achieved with 5 mM disodium hydrogen phosphate buffer at pH 10.4. A linear calibration graph over VO₃ ^? and V(IV) with concentration ranges 5–15 mg L^?1 gave the detection limit at 0.09 and 0.1 mg L^?1, respectively. Both V(IV) and V(V) were successfully determined in Benfield sample, with concentrations of V(IV) and V(V) at 4 and 11,000 mg L^?1, respectively.     

Spectrophotometric determination of vanadium(IV) in the presence of vanadium(V) using Br-PADAP

In the present paper, a simple and sensitive method is proposed for vanadium(IV) determination in the presence of vanadium(V). This is based on the oxidation of vanadium(IV) present in the sample to vanadium(V) by addition of iron(III) cation, followed by a complexation reaction of iron(II) with the spectrophotometric reagent 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP). The iron(II) reacts with Br-PADAP immediately, forming a stable complex with a large molar absorptivity. The vanadium(IV) determination is possible, with a calibration sensitivity of 0.549 g ml^–1, for an analytical curve of 18.8 ng ml^–1 to 2.40 g ml^–1, molar absorptivity of 2.80 × 10⁴ 1 mole^–1 cm^–1 and a detection limit of 5.5 ng ml^–1. Selectivity was increased with the use of EDTA as a masking agent. The proposed method was applied for the vanadium(IV) determination in the presence of several amounts of vanadium(V). The results revealed that 200 g of vanadium(V) do not interfere with determination of 5.00 g of vanadium(IV). The precision and the accuracy obtained were satisfactory (R. S. D.<2%).     

Rapid and simple chromatographic separation of V(V) and V(IV) using KH-phthalate and their determination by flame atomic absorption spectrometry

A method was developed for the chromatographic separation of V(V) and V(IV) based on the different sorption forces of these vanadium species in C18 columns in presence of KH-phthalate. The vanadium species were detected with a flame atomic absorption spectrometer with acetylene/N₂O flame. The detection limits (3σ) of V(V) and V(IV) were 0.18 μg/mL and 0.15 μg/mL, respectively. The relative standard deviations (N = 5) are 4.2% and 3.4% for 20–20 μg/mL V(V) and V(IV), respectively. The sampling frequency is 75/h. Because of the special interaction occurring between phthalate and V(IV) on the C18 column and the acetylene/N₂O flame atomic absorption detection, practically no interferences can be detected even in large inorganic matrix.     

Speciation of vanadium in oilsand coke and bacterial culture by high performance liquid chromatography inductively coupled plasma mass spectrometry

A simple and sensitive method for the speciation of vanadium(III), (IV), and (V) was developed by using high performance liquid chromatography and inductively coupled plasma mass spectrometry (HPLC-ICPMS). The EDTA-complexed vanadium species were separated on a strong anion exchange column with an eluent containing 2 mM EDTA, 3% acetonitrile, and 80 mM ammonium bicarbonate at pH 6. Each analysis was complete in 5 min. The detection limits were 0.6, 0.7 and 1.0 μg L⁻¹ for V(III), V(IV), and V(V), respectively. The method was applied to coke pore water samples from an oilsand processing/upgrading site in Fort McMurray, Alberta, Canada and to Shewanella putrefaciens CN32 bacterial cultures incubated with V(V). In the coke pore water samples, V(IV) and V(V) were found to be the major species. For the first time, V(III) was detected in the bacterial cultures incubated with V(V).     

Hollow-fibre liquid phase microextraction for separation and preconcentration of vanadium species in natural waters and their determination by electrothermal vaporization-ICP-OES

For separation and determination of vanadium(IV/V) species, a fast and sensitive method by combining hollow-fibre liquid phase microextraction (HF-LPME) with electrothermal vaporization (ETV)-ICP-OES has been developed. Two vanadium species (V(IV) and V(V)) were separated by HF-LPME with the use of ammonium pyrrolidinecarbodithioate (APDC) as chelating agent for complexing with different V species and carbon tetrachloride as the extraction solvent, and the vanadium in the post-extraction organic phase was injected into the graphite furnace for ETV-ICP-OES detection, in which APDC was acted as the chemical modifier. At pH 5.0, both V(IV)-APDC and V(V)-APDC were extracted quantitatively into CCl₄ for determination of total V. For speciation studies, 1,2-cyclohexanediaminetetraacetic acid (CDTA) was added to the sample for masking V(IV), so that only V(V)-APDC was extracted and determined. The concentration of V(IV) was calculated by subtracting the V(V) concentration from the total concentration of V. Under the optimized experimental conditions, the enrichment factor was 74 and the detection limits for V(IV) and V(V) were 86 pg mL⁻¹ and 71 pg mL⁻¹, respectively. The proposed method has been applied to the speciation of V in environmental water samples, and the recovery was in the range of 94%-107%. The results show that V(V) is the dominant existence form in oxygenic water and V(IV) could not been detected. In order to validate the developed procedure, a NIES No.8 vehicle exhaust particulates certified reference material was analyzed, and the results obtained for total vanadium are in good agreement with the certified values. The proposed method is simple, rapid, selective, and sensitive and no oxidation/reduction is required, it is applicable to the speciation of vanadium in environmental samples with the complicated matrix.     

Modeling Speciation and Solubility in Aqueous Systems Containing U(IV,VI), Np(IV,V, VI), Pu(III,IV, V,VI), Am(III), and Cm(III)

A comprehensive thermodynamic model, referred to as the Mixed-Solvent Electrolyte model, has been applied to calculate phase equilibria and chemical speciation in selected aqueous actinide systems. The solution chemistry of U(IV, VI), Np(IV, V, VI), Pu(III, IV, V, VI), Am(III), and Cm(III) has been analyzed to develop the parameters of the model. These parameters include the standard-state thermochemical properties of aqueous and solid actinide species as well as the ion interaction parameters that reflect the solution’s nonideality. The model reproduces the solubility behavior and accurately predicts the formation of competing solid phases as a function of pH (from 0 to 14 and higher), temperature (up to 573 K), partial pressure of CO₂ (up to \( p_{{{\text{CO}}_{2} }} \)  = 1 bar), and concentrations of acids (to 127 mol·kg^?1), bases (to 18 mol·kg^?1), carbonates (to 6 mol·kg^?1) and other ionic components (i.e., Na⁺, Ca²⁺, Mg²⁺, OH^?, Cl^?, \( {\text{ClO}}_{4}^{ - } \), and \( {\text{NO}}_{3}^{ - } \)). Redox effects on solubility and speciation have been incorporated into the model, as exemplified by the reductive and oxidative dissolution of Np(VI) and Pu(IV) solids, respectively. Thus, the model can be used to elucidate the phase and chemical equilibria for radionuclides in natural aquatic systems or in nuclear waste repository environments as a function of environmental conditions. Additionally, the model has been applied to systems relevant to nuclear fuel processing, in which nitric acid and nitrate salts of plutonium and uranium are present at high concentrations. The model reproduces speciation and solubility in the U(VI) + HNO₃ + H₂O and Pu(IV, VI) + HNO₃ + H₂O systems up to very high nitric acid concentrations (\( x_{{{\text{HNO}}_{3} }} \approx 0.70 \)). Furthermore, the similarities and differences in the solubility behavior of the actinides have been analyzed in terms of aqueous speciation.     

Column chromatographic speciation of chromium for Cr(VI) and several species of Cr(III)

Summary Chromium can be present in aqueous solution as Cr(VI) or in monomeric, dimeric, trimeric and higher polymeric forms of Cr(III). Many monomeric forms of Cr(III) are possible, with the water molecules of Cr(H₂O) ₆ ³⁺ substituted by anionic or neutral species. This proliferation of Cr(III) species makes the complete speciation of chromium a continuing challenge to the analyst. A simple and effective cation exchange procedure for the separation of various of these species uses a small glass column containing 1 mL of pre-treated cation exchange resin (Na⁺ form). Stepwise elution with solutions of perchloric acid, Ca²⁺ (pH=2) and La³⁺ (pH=2) separates Cr(VI) and seven Cr(III) species from CrX₃ to tetramer. Radiometric (Cr-51), spectrophotometric and other detection methods can be employed; the use of radiochromium gives the lowest detection limit.     

Separation and preconcentration of U(VI) on XAD-4 modified with 8-hydroxy quinoline

Amberlite XAD-4 adsorber resin was modified with 8-hydroxy quinoline (Oxine) by equilibrating with methanol solution of the reagent and the modified resin was used as a support material for the solid phase extraction and preconcentration of UO₂²⁺ from aqueous solution at pH between 4 and 5.5. Ten micrograms of uranium from 300 ml of aqueous phase could be quantitatively extracted in to 1 g of the modified resin giving an enrichment of 200. Uranium collected in the column could be eluted out with methanol-HCl mixture and determined spectrophotometrically using arsenazo(III) as the chromogenic reagent. The preconcentration could be made selective to uranium by using EDTA as a masking agent for transition metal ions and Th(IV).     

An Aqueous Thermodynamic Model for the Complexation of Sodium and Strontium with Organic Chelates Valid to High Ionic Strength. I. Ethylenedinitrilotetraacetic Acid (EDTA)

An aqueous thermodynamic model is developed, which accurately describes the effects of Na⁺ complexation, ionic strength, carbonate concentration, and temperature on the complexation of Sr²⁺ by ethylenedinitrilotetraacetic acid (EDTA) under basic conditions. The model is developed from the analysis of literature data on apparent equilibrium constants, enthalpies, and heat capacities, as well as on an extensive set of solubility data on SrCO₃(c) in the presence of EDTA obtained as part of this study. The solubility data for SrCO₃(c) were obtained in solutions ranging in Na₂CO₃ concentration from 0.01 to 1.8 m, in NaNO₃ concentration from 0 to 5 m, and at temperatures extending to 75C. The final aqueous thermodynamic model is based upon the equations of Pitzer and requires the inclusion of a NaEDTA^3– species. An accurate model for the ionic strength dependence of the ion-interaction coefficients for the SrEDTA^2– and NaEDTA^3–aqueous species allows the extrapolation of standard state equilibrium constants for these species, which are significantly different from the 0.1 m reference state values available in the literature. The final model is tested by application to chemical systems containing competing metal ions (i.e., Ca²⁺) to further verify the proposed model and indicate the applicability of the model parameters to chemical systems containing other divalent metal-EDTA complexes.     

Rapid and simple chromatographic separation of V(V) and V(IV) using KH-phthalate and their determination by flame atomic absorption spectrometry

A method was developed for the chromatographic separation of V(V) and V(IV) based on the different sorption forces of these vanadium species in C18 columns in presence of KH-phthalate. The vanadium species were detected with a flame atomic absorption spectrometer with acetylene/N₂O flame. The detection limits (3σ) of V(V) and V(IV) were 0.18 μg/mL and 0.15 μg/mL, respectively. The relative standard deviations (N = 5) are 4.2% and 3.4% for 20–20 μg/mL V(V) and V(IV), respectively. The sampling frequency is 75/h. Because of the special interaction occurring between phthalate and V(IV) on the C18 column and the acetylene/N₂O flame atomic absorption detection, practically no interferences can be detected even in large inorganic matrix. Received: 20 February 1997 / Revised: 2 June 1997 / Accepted: 7 June 1997     

Aqueous polymerization of acrylamide initiated by cerium (IV)–ethylenediamine tetraacetic acid redox system

Ethylenediamine tetraacetic acid (EDTA) terminated polyacrylamide was obtained by using the EDTA–cerium(IV) ammonium nitrate [Ce(IV)] redox initiator in the aqueous polymerization of acrylamide. The polymerization behaviors as a function of the concentration of Ce(IV), EDTA, and acrylamide as well as temperature were studied. The consumption rate of cerium(IV) depends a first-order reaction on the ceric ion concentration ([Ce(IV)]). The complex formation constant (K) and disproportionation constant (k_d) of Ce(IV)–EDTA chelated complex are 1.67 × 10⁴ and 3.77 × 10^?3, respectively. The rate dependences of polymerization on monomer concentration and EDTA concentration both follow a second-order reaction in the run of initial monomer concentration ([M]_i) equal to 0.2 mol dm^?3. The number average molecular weight increases linearly with the ratio of [M]_i/[Ce(IV)]_i. The mechanism and kinetics for the polymerization was proposed. The kinetic parameters involved were determined. © 1992 John Wiley & Sons, Inc.     

The leaching of V(V) with PO4 in the speciation analysis of soil

The leaching of V(V) from soil by two phosphate reagents, viz. (NH₄)₂HPO₄ and Na₃PO₄ has been studied. (NH₄)₂HPO₄ (1 M) and Na₃PO₄ (0.01 M) were efficient enough to extract all V(V) species from samples. The results were compared with that extracted by Na₂CO₃. Statistical evaluations show that the proposed method is similar to the established method utilizing Na₂CO₃.The method was applied in the analysis of soil samples from contaminated area of the vanadium mine where many grazing cattle died.Validation of the method was also done by comparing the sum of V(IV) and V(V) and the total vanadium obtained from the samples by an independent method. It was found that the sum of V(V) and V(IV) is in good agreement with the total content of vanadium in all samples after HF-H₂SO₄-HClO₄ digestion. From the results of the investigation, it follows that the use of phosphate fertilizers in V(V)-rich soil may enhance the mobility and availability of V(V) to plants. The plants, in turn, are consumed by animals that may die depending on the level of poisoning.     

Catalytic Adsorptive Stripping Voltammetry of Germanium(IV) in the Presence of Gallic Acid and Vanadium(IV)‐EDTA

A highly sensitive and selective catalytic adsorptive cathodic striping procedure for the determination of trace germanium is presented. The method is based on adsorptive accumulation of the Ge(IV)‐gallic acid (GA) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species. The reduction current is enhanced catalytically by addition of vanadium(IV)‐EDTA. The optimal experimental conditions include the use of 0.03 mol/L HClO₄ (pH1.6), 6.0×10^?3 mol/L GA, 3.0×10^?3 mol/L V(IV), 4.0×10^?3 mol/L EDTA, an accumulation potential of ?0.10 V(vs. Ag/AgCl), an accumulation time of 120 s and a differential pulse potential scan mode. The peak current is proportional to the concentration of Ge(IV) over the range of 3.0×10^?11 to 1.0×10^?8 mol/L and the detection limit is 2×10^?11 mol/L for a 120 s adsorption time. The relative standard deviation at 5.0×10^?10 mol/L level is 3.1%. No serious interferences were found. The method was applied to the determination of germanium in ore, mineral water and vegetable samples with satisfactory results.     

Investigation on Concentrated Ⅴ（Ⅳ）/Ⅴ（Ⅴ） Redox Reaction by Rotating Disc Voltammetry

The kinetic characteristics of the concentrated Ⅴ（Ⅳ）/Ⅴ（Ⅴ） couple have been studied at a glassy carbon electrode in sulfuric acid using rotating-disc electrode and cyclic voltammetry. The kinetics of the Ⅴ（Ⅳ）/Ⅴ（Ⅴ） redox couple reaction was found to be electrochemically quasi-reversible with the slower kinetics for the Ⅴ（Ⅴ） reduction than that for the Ⅴ（Ⅳ） oxidation. And, dependence of diffusion coefficients and kinetic parameters of Ⅴ（Ⅳ） species on the Ⅴ（Ⅳ） and H2SO4 concentration was investigated. It is shown that the concentration of active species Ⅴ（Ⅳ） should be over 1 mol·L^-1 for the redox flow battery application. Further, with increasing the Ⅴ（Ⅳ） and H2SO4 concentration, the diffusion coefficients of Ⅴ（Ⅳ） were gradually reduced whereas its kinetics was improved considerably, especially in the case of Ⅴ（Ⅳ） and H2SO4 up to 2 and 4 mol·L^-1.     

V2O5/TiO2 Catalyst Xerogels: Method of Preparation and Characterization

This work describes a modified sol-gel method for the preparation of V₂O₅/TiO₂ catalysts. The samples have been characterized by N₂ adsorption at 77 K, X-ray Diffractometry (XRD), Scanning Electronic Microscopy (SEM/EDX) and Fourier Transform Infrared Spectroscopy (FT-IR). The surface area increases with the vanadia loading from 24 m² g^–1 for pure TiO₂ to 87 m² g^–1 for 9 wt% of V₂O₅. The rutile form is predominant for pure TiO₂ but becomes enriched with anatase phase when vanadia loading is increased. No crystalline V₂O₅ phase was observed in the diffractograms of the catalysts. Analysis by SEM showed heterogeneous granulation of particles with high vanadium dispersion. Two species of surface vanadium were observed by FT-IR spectroscopy: a monomeric vanadyl and polymeric vanadates. The vanadyl/vanadate ratio remains practically constant. Ethanol oxidation was used as a catalytic test in a temperature range from 350 to 560 K. The catalytic activity starts around 380 K. For the sample with 9 wt% of vanadia, the conversion of ethanol into acetaldehyde as the main product was approximately 90% at 473 K.     

Synthesis,spectral and electrochemical studies of alkoxo-bonded mixed-ligand oxovanadium(IV) and oxovanadium(V) complexes incorporating tridentate ONO donor azophenolalcoholate/aldiminealcoholates

Mixed-ligand vanadyl(IV) and vanadyl(V) complexes with tridentate ONO donor azophenolalcoholate/aldiminealcoholates [viz., 2-hydroxy-2-hydroxymethyl-5-methylazobenzene (H₂L¹), N-(2-hydroxymethylphenyl)-salicylaldimine (H₂L²) and N-(2-hydroxymethylphenyl)1-hydroxy-2-naphthaldimine (H₂L³)] and bidentate NN [viz., 2,2-bipyridine (bipy) and 1,10-phenanthroline (phen)] or NO [viz., 8-hydroxyquinoline (Hhq)] donor ligands have been prepared and characterized by elemental analyses and by i.r., e.p.r. and u.v.–vis. spectroscopies. The data show that the vanadyl(IV) complexes exist in two isomeric solid forms viz., monomers and polymers, whereas vanadyl(V) complexes exist only in the monomeric form. The polymeric structure results from intermolecular V=OV=O interactions. The complexes with NN donor ligands are one electron paramagnetic and display two ligand-field transitions in the visible region, whereas the complexes with ON donor ligands are diamagnetic and exhibit only LMCT bands. The vanadyl(IV) complexes display an irreversible oxidation peak near +0.30 V for complexes with (L¹)^2– and near +0.55 V for complexes with (L²)^2– and (L³)^2– ligands, while the vanadyl(V) complexes display a quasi-reversible one electron reduction couple near –0.23 V versus s.c.e. The trends in the (V=O), values for the visible region transitions and the redox potential values for the vanadyl(IV) complexes have been scrutinized.