Flavonol Derivatives for Determination of Cr(III) and W(VI)

 Simple, rapid, sensitive and selective methods for the determination of Cr(III) and W(VI) with flavonol derivatives in the presence of surface-active agents are proposed. In the pH ranges 3.4–4.2 and 1.9–2.5, the molar absorptivities of Cr(III)-morin-emulsifier S (EFA) and W(VI)-morin-polyvinylpyrrolidone (PVP) systems are 1.13×10⁵ and 2.13×10⁴ L mol⁻¹ cm⁻¹ at 435 and 415 nm, respectively. The Cr(III)-quercetin-PVP and W(VI)-quercetin-cetylpyridinium bromide (CPB) systems are formed in the pH ranges 4–4.6 and 2.2–2.8 with molar absorptivities 1.02×10⁵ and 9.02×10⁴ L. mol⁻¹ cm⁻¹ at 441 and 419 nm, respectively. The linear dynamic ranges for the determination of Cr(III) and W(VI) with morin in the presence of EFA and PVP are 0.03–0.46 and 0.71–8.1 μg mL⁻¹, respectively. The corresponding ranges with quercetin are 0.04–0.54 and 0.14–2.1 μg mL⁻¹ of Cr(III) and W(VI), respectively. The r.s.d (n = 10) for the determination of 0.25 and 3.7 μg mL⁻¹ of Cr(III) and W(VI) with morin and their detection limits are 0.88 and 0.99% and 0.016 and 0.63 μg mL⁻¹, respectively. Using quercetin, the r.s.d (n = 10) for 0.22 and 1.2 μg mL⁻¹ of Cr(III) and W(VI) and their detection limits are 0.92 and 0.91% and 0.015 and 0.08 μg mL⁻¹, respectively. The critical evaluation of the proposed methods is performed by statistical analysis of the experimental data. The proposed methods are applied to determine Cr in steel, non-ferrous alloys, wastewater and mud filtrate and to the determination of W in steel. Received March 8, 1999. Revision January 21, 2000.     

Application of double-spike isotope dilution for the accurate determination of Cr(III), Cr(VI) and total Cr in yeast

A method is presented for the simultaneous determination of Cr(III) and Cr(VI) in yeast using species-specific double-spike isotope dilution (SSDSID) with anion-exchange liquid chromatography (LC) separation and sector field inductively coupled plasma mass spectrometric (SF-ICP-MS) detection. Total Cr is quantitated using ID SF-ICP-MS. Samples were digested on a hot plate at 95±2 °C for 6 h in an alkaline solution of 0.5 M NaOH and 0.28 M Na₂CO₃ for the determination of Cr(III) and Cr(VI), whereas microwave-assisted decomposition with HNO₃ and H₂O₂ was used for the determination of total Cr. Concentrations of 2,014±16, 1,952±103 and 76±48 mg kg⁻¹ (one standard deviation, n=4, 3, 3), respectively were obtained for total Cr, Cr(III) and Cr(VI) in the yeast sample. Significant oxidation of Cr(III) to Cr(VI) (24.2±7.6% Cr(III) oxidized, n=3) and reduction of Cr(VI) to Cr(III) (37.6±6.5% Cr(VI) reduced, n=3 ) occurred during alkaline extraction and subsequent chromatographic separation at pH 7. Despite this significant bidirectional redox transformation, quantitative recoveries for both Cr(III) and Cr(VI) were achieved using the SSDSID method. In addition, mass balance between total Cr and the sum of Cr(III) and Cr(VI) concentrations was achieved. Method detection limits of 0.3, 2 and 30 mg kg⁻¹ were obtained for total Cr, Cr(VI) and Cr(III), respectively, based on a 0.2-g sub-sample.     

Speciation of chromium in water using crosslinked chitosan-bound FeC nanoparticles as solid-phase extractant, and determination by flame atomic absorption spectrometry

Crosslinked chitosan-bound FeC nanoparticles (CCBFeCNP) were prepared, and the adsorptive behavior of Cr(III) and Cr(VI) on CCBFeCNP were assessed. At pH 6.0–10.0, CCBFeCNP is selective towards Cr(III) but hardly selective towards Cr(VI). The retained Cr(III) is subsequently eluted with 0.5 mol L⁻¹ HCl. Total chromium is determined after reduction of Cr(VI) to Cr(III) by ascorbic acid. A new method of flow injection using a micro-column packed with CCBFeCNP as solid phase extractant has been developed for speciation of Cr(III) and Cr(VI) in water samples, followed by flame atomic absorption spectrometry. The effects of pH, sample flow rate and volume, elution solution and interfering ions on the recoveries of Cr(III) were systematically investigated. Under optimum conditions, the adsorption capacity of CCBFeCNP for Cr(III) is 10.5 mg g⁻¹ at pH 7.5. The procedure presented was applied to chromium speciation in water samples, and the results were satisfactory.     

Preconcentration and separation of Cr(III) and Cr(VI) using sawdust as a sorbent

A simple, inexpensive method based on solid-phase extraction (SPE) on sawdust from Cedrus deodera has been developed for speciation of Cr(III) and Cr(VI) in environmental water samples. Because different exchange capacities were observed for the two forms of chromium at different pH—Cr(III) was selectively retained at pH 3 to 4 whereas Cr(VI) was retained at pH 1—complete separation of the two forms of chromium is possible. Retained species were eluted with 2.5 mL 0.1 mol L⁻¹ HCl and 0.1 mol L⁻¹ NaOH. Detection limits of 0.05 and 0.04 μg mL⁻¹ were achieved for Cr(III) and Cr(VI), respectively, with enrichment factors of 100 and 80. Recovery was quantitative using 250 mL sample volume for Cr(III) and 200 mL for Cr(VI). Different kinetic and thermodynamic properties that affect sorption of the chromium species on the sawdust were also determined. Metal ion concentration was measured as the Cr(VI)–diphenylcarbazide complex by UV–visible spectroscopy. The method was successfully applied for speciation of chromium in environmental and industrial water samples.     

Chemiluminescence determination of chromium(III) and total chromium in water samples using the periodate-lucigenin reaction

A new chemiluminescence (CL) method combined with flow injection technique is described for the determination of Cr(III) and total Cr. It is found that a strong CL signal is generated from the reaction of Cr(III), lucigenin and KIO₄ in alkaline condition. The determination of total Cr is performed by pre-reduction of Cr(VI) to Cr(III) by using H₂SO₃. The CL intensity is linearly related to the concentration of Cr in the range 4.0 × 10⁻¹⁰–1.0 × 10⁻⁶ g mL⁻¹. The detection limit (3s _b) is 1 × 10⁻¹⁰ g mL⁻¹ Cr and the relative standard deviation is 1.9% (5.0 × 10⁻⁸ g mL⁻¹ of Cr(III) solution, n = 11). The method was applied to the determination of Cr(III) and total Cr in water samples and compared satisfactorily with the official method.     

Equilibrium and kinetics study of Gd(III) and U(VI) adsorption from aqueous solutions by modified Sorrel’s cement

Modified Sorrel’s cement was prepared by the addition of ferric chloride. The modified cement (MF5) was analyzed and characterized by different methods. Adsorption of Gd(III) and U(VI) ions in carbonate solution has been studied separately as a function of pH, contact time, adsorbent weight, carbonate concentration, concentration of Gd(III) and U(VI) and temperature. From equilibrium data obtained, the values of Δ H, Δ S and Δ G were found to equal −30.9 kJ ⋅ mol⁻¹, −85.4 J ⋅ mol⁻¹ ⋅,K⁻¹, and −5.4 KJ ⋅ mol⁻¹, respectively, for Gd(III) and 18.9 kJ ⋅ mol⁻¹, 67.8 J ⋅ mol⁻¹ K⁻¹ and −1.3 KJ ⋅ mol⁻¹, respectively, for U(VI). The equilibrium data obtained have been found to fit both Langmuir and Freundlich adsorption isotherms. The batch kinetic of Gd(III) and U(VI) on modified Sorrel’s cement (MF5) with the thermodynamic parameters from carbonate solution were studied to explain the mechanistic aspects of the adsorption process. Several kinetic models were used to test the experimental rate data and to examine the controlling mechanism of the adsorption process. Various parameters such as effective diffusion coefficient and activation energy of activation were evaluated. The adsorption of Gd(III) and U(VI) on the MF5 adsorbent follows first-order reversible kinetics. The forward and backward constants for adsorption, k ₁and k ₂ have been calculated at different temperatures between 10 and 60^∘C. Form kinetic study, the values of Δ H ^* and Δ S ^* were calculated for Gd(III) and U(VI) at 25^∘C. It is found that Δ H ^* equals −14.8 kJmol⁻¹ and 7.2 kJmol⁻¹ for Gd(III) and U(VI), respectively, while Δ S ^* were found equal −95.7 Jmol⁻¹K⁻¹ and −70.5 Jmol⁻¹K⁻¹ for Gd(III) and U(VI), respectively. The study showed that the pore diffusion is the rate limiting for Gd(III) and (VI).     

Adsorption of Cu(II), Cd(II), Pb(II), Cr(VI) by double hydroxides on the basis of Al oxide and Zr, Sn, and Ti oxides

It was studied the equilibrium adsorption and adsorption kinetics of Cu(II), Cd(II), Pb(II), and Cr(VI) by composite hydroxides formed by Me _x O _y · nH₂O and Me_0.4–0.7Al_0.6–0.3O _y · nH₂O, where Me = Zr, Sn and Ti. It was estimated the values of the diffusion coefficients of adsorbed ions Cu(II) and Cr(VI) from kinetic values. It was established that the estimated diffusion coefficients of adsorbed ions Cu(II) are in the range 0.4 × 10⁻¹²–2.5 × 10⁻¹² m²/s for individual hydroxides and 1.2 × 10⁻¹²–2.8 × 10⁻¹² m²/s for double hydroxides. The obtained values of diffusion coefficients Cr (VI) for double hydroxides are 0.1 × 10⁻¹⁰–0.4 × 10⁻¹⁰ m²/s.     

An “off–on” fluorescence probe for chromium(III) ion determination in aqueous solution

An “off–on” rhodamine-based fluorescence probe for the selective signaling of Cr(III) has been designed by exploiting the guest-induced structure transform mechanism. This system shows a sharp Cr(III)-selective fluorescence enhancement response in 100% aqueous system under physiological pH value and possesses high selectivity against the background of environmentally and biologically relevant metal ions including Cr(VI), Al(III), Fe(III), Cd(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I). Under optimum conditions, the fluorescence intensity enhancement of this system is linearly proportional to Cr(III) concentration from 5.0 × 10⁻⁸ to 7.0 × 10⁻⁶ mol L⁻¹ with a detection limit of 1.6 × 10⁻⁸ mol L⁻¹.     

Chromium(III) Hydroxide Solubility in the Aqueous K+-H+-OH?-CO2-HCO 3? -CO 32? -H2O System: A?Thermodynamic Model

Chromium(III)-carbonate reactions are expected to be important in managing high-level radioactive wastes. Extensive studies on the solubility of amorphous Cr(III) hydroxide solid in a wide range of pH (3–13) at two different fixed partial pressures of CO₂(g) (0.003 or 0.03 atm.), and as functions of K₂CO₃ concentrations (0.01 to 5.8 mol⋅kg⁻¹) in the presence of 0.01 mol⋅dm⁻³ KOH and KHCO₃ concentrations (0.001 to 0.826 mol⋅kg⁻¹) at room temperature (22±2 °C) were carried out to obtain reliable thermodynamic data for important Cr(III)-carbonate reactions. A combination of techniques (XRD, XANES, EXAFS, UV-Vis-NIR spectroscopy, thermodynamic analyses of solubility data, and quantum mechanical calculations) was used to characterize the solid and aqueous species. The Pitzer ion-interaction approach was used to interpret the solubility data. Only two aqueous species [Cr(OH)(CO₃)₂²⁻ and Cr(OH)₄CO₃³⁻] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO₂(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support the existence of these species. The log ₁₀ K° values of reactions involving these species [{Cr(OH)₃(am) + 2CO₂(g)⇌Cr(OH)(CO₃)₂²⁻+2H⁺} and {Cr(OH)₃(am) + OH⁻+CO₃²⁻ ⇌Cr(OH)₄CO₃³⁻}] were found to be −(19.07±0.41) and −(4.19±0.19), respectively. No other data on any Cr(III)-carbonato complexes are available for comparisons.     

Determination of Kinetic Parameters in the Biosorption of Cr (VI) on Immobilized <Emphasis Type="Italic">Bacillus cereus</Emphasis> M<Superscript>1</Superscript><Subscript>16</Subscript> in a Continuous Packed Bed Column Reactor

Due to technological advancement, environment suffers from untreated toxic heavy metal bearing effluent coming from different industries. Chromium (VI) is one of those heavy metals having adverse impact on ecological balance, human, and plant health because of its carcinogenic properties. Biosorption is presented as an alternative to traditional technologies which are costly and inefficient for treatment of industrial wastes containing low amount of heavy metals. In this study, bioremediation of Cr (VI) ions by immobilized Bacillus cereus M¹ ₁₆ was investigated in a laboratory scale packed bed up-flow column reactor. The effect of important parameters, such as the inlet flow rate, influent concentration, and effective bed height, has been studied. External mass transfer, surface adsorption, and intrabead mass transfer were also studied to conclude the rate limiting step for removal of Cr (VI) and to determine the process parameters which are important for biosorption optimization. The external mass transfer coefficient was calculated at different flow rates (6.51 × 10⁻² to 7.58 × 10⁻² cm/min). Using the model, the surface adsorption rate constant (k _ad) and the intrabead mass transfer coefficient (k _i) were predicted as 0.0267 × 10⁻³ and 0.7465 × 10⁻³ l/g/min, respectively. Both are much lower than the external mass transfer coefficient (k _e). The surface adsorption phenomenon is acting as the rate-limiting step due to its high resistance for removal of Cr (VI).     

A catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances

A simple and fast catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances has been developed. The procedure for chromium determination in the presence of DTPA and nitrates was employed as the initial method. In order to enhance the selectivity vs. Cr(III) the measurements were performed at 40°C. Interference from dissolved organic matter such as humic and fulvic acids was drastically decreased by adding Amberlite XAD-7 resin to the voltammetric cell before the deaeration step. The whole procedure was applied to a single cell, which allowed monitoring of the voltammetric scan. Optimum conditions for removing humic and fulvic acids due to their adsorption on XAD-7 resin were evaluated. The use of XAD-7 resin also minimize interferences from various cationic, anionic, and nonionic surfactants. The calibration graph for Cr(VI) for an accumulation time of 30 s was linear in the range 5 × 10⁻¹⁰ to 5 × 10⁻⁸ mol L⁻¹. The relative standard deviation for determination of Cr(VI) at a concentration of 1 × 10⁻⁸ mol L⁻¹ was 3.5% (n = 5). The detection limit estimated from 3 times the standard deviation for low Cr(VI) concentrations and an accumulation time of 30 s was about 1.3 × 10⁻¹⁰ mol L⁻¹. The proposed method was successfully applied to Cr(VI) determination at trace levels in soil samples.     

Separation and Removal of Metal Ionic Species by Polymer Inclusion Membranes

Competitive alkali metal cation transport across polymer inclusion membranes (PIMs) containing sym-(alkyl)dibenzo-16-crown-5-oxyacetic acid carriers provides excellent selectivity for Na⁺ transport with the total fluxes being strongly influenced by the length of the alkyl chain that is attached geminal to the functional side arm in the lariat ether. Removal of chromium(VI) anions by PIMs from acidic aqueous phases was also investigated. Using tri-n-octylamine (TOA) as the ion carrier, Cr(VI) was removed by a PIM to decrease the source phase metal concentration from 1.0 to 0.010 ppm after 30 hours of transport. Competitive transport of Cr(VI) and Cr(III) ions from acidic source phases through PIMs and supported liquid membranes (SLMs) containing TOA and tri-n-octylphosphine oxide (TOPO) as carriers was evaluated and a very high Cr(VI)/Cr(III) separation ratio of 4800 was achieved with a PIM containing TOA. Competitive transport of Zn(II), Cd(II), and Cr(VI) from acidic aqueous solutions through PIMs containing TOA was investigated. The selectivity order for metal ion transport was: HCrO₄ ^–>CdCl₄ ^2–+CdCl₃ ^–>ZnCl₄ ^2–+ ZnCl₃ ^–. Non-contact atomic force microscopy was used to obtain images of the pores in cellulose triacetate membranes containing a plasticizer.     

<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-Butylcalix[8]arene loaded silica gel for preconcentration of uranium(VI) via solid phase extraction

This paper reports silica gel loaded with p-tert-butylcalix[8]arene as a new solid phase extractor for determination of trace level of uranium. Effective extraction conditions were optimized in column methods prior to determination by spectrophotometry using arsenazo(III). The results showed that U(VI) ions can be sorbed at pH 6 in a mini-column and quantitative recovery of U(VI) (>95–98%) was achieved by stripping 0.4 mol L⁻¹ HCl. The sorption capacity of the functionalized sorbent is 0.072 mmol uranium(VI) g⁻¹ modified silica gel. The relative standard deviation and detection limit were 1.2% (n = 10) for 1 μg uranium(VI) mL⁻¹ solution and 0.038 μg L⁻¹, respectively. The method was employed to the preconcentration of U(VI) ions from spiked ground water samples.     

Adsorption of chromium from aqueous solution using chitosan beads

A basic investigation on the removal of Cr(III) and Cr(VI) ions from aqueous solution by chitosan beads was conducted in a batch adsorption system. The chitosan beads were prepared by casting an acidic chitosan solution into an alkaline solution. The influence of different experimental parameters; pH, agitation period and different concentration of Cr(III) and Cr(VI) ions was evaluated. A pH 5.0 was found to be an optimum pH for Cr(III) adsorption, and meanwhile pH 3.0 was the optimum pH for the adsorption of Cr(VI) onto chitosan beads. The Langmuir and Freundlich adsorption isotherm models were applied to describe the isotherms and isotherm constants for the adsorption of Cr(III) and Cr(VI) onto chitosan beads. Results indicated that Cr(III) and Cr(VI) uptake could be described by the Langmuir adsorption model. The maximum adsorption capacities of Cr(III) and Cr(VI) ions onto chitosan beads were 30.03 and 76.92 mg g⁻¹, respectively. Results showed that chitosan beads are favourable adsorbents. The Cr(III) and Cr(VI) ions can be removed from the chitosan beads by treatment with an aqueous EDTA solution.     

Optical and electrochemical sol-gel sensors for inorganic species

The use of sol-gels as a sensing matrix for the development of unique sensing strategies is discussed. Sol-gels offer almost limitless possibilities for sensing substrates due to the variety of physical properties that can be obtained by altering a number of discussed fabrication conditions and techniques. By careful consideration of the sensing requirements, novel detection methods have been developed for a variety of analytes and applications. Here, sol-gels have been used to monitor pH at the extreme ends of the scale ([H⁺] = 1–11 M and [OH⁻] = 1–10 M) and in mixed solvent/solute systems using dual sensing approaches. The use of ligand-grafted sol-gel monoliths for optical determination of metal ion species is also discussed. The electrochemical determination of Cr(VI) by electrodeposited sol-gel modified electrodes is also presented.     

Catalytic Spectrophotometric Determination of Molybdenum

Summary.  A highly selective, sensitive, and simple catalytic method for the determination of molybdenum in natural and waste waters was developed. It is based on the catalytic effect of Mo(VI) on the oxidation of 2-aminophenol with H₂O₂. The reaction is monitored spectrophotometrically by tracing the oxidation product at 430 nm after 10 min of mixing the reagents. Addition of 800 μg · cm⁻³ EDTA conferred high selectivity; however, interfering effects of Au(III), Cr(III), Cr(VI), and Fe(III) had to be eliminated by a reduction and co-precipitation procedure with SnCl₂ and Al(OH)₃. Mo(VI) shows a linear calibration graph up to 11.0 ng · cm⁻³; the detection limit, based on the 3S _b-criterion, is 0.10 ng · cm⁻³. The unique selectivity and sensitivity of the new method allowed its direct application to the determination of Mo(VI) in natural and waste waters. Received April 11, 2001. Accepted (revised) June 18, 2001     

Introduction to the dynamic theory of the (H+, e−) couple insertion in γ-MnO2

This paper presents a phenomenological theory of coupled H⁺ and e⁻ diffusion in γ/ɛ-MnO₂. A set of five dynamic regimes governs the (H⁺, e⁻) insertion during the entire reduction (0.08 < r < 1) of the dioxide. It is imposed by a global balance of several physical quantities which depend on the reduction level r. The principal potential factor for the diffusion in a given direction is the difference between the components, along this direction, of the self velocities V _e− and V _H+. The longitudinal component E _ld of the internal electric field vector E _d plays, with respect to electrons and protons, the velocity regulator role. The transversal component E _td allows some homogenisation of (H⁺,e⁻) concentration during the first half of the reaction and trapping of electrons in the second half. Towards r≈ 0.50, V _e− and V _H+ are equal, the internal electric field reverses its orientation after taking a null value and the first Mn³⁺ ions appear. This introduction to the dynamic theory of γ/ɛ-MnO₂ is a new finding and can interpret most of its physical/chemical properties, especially the behaviour change around r≈ 0.50. Received: 11 November 1998 / Accepted: 25 March 1999     

A potential harmonic method for the three-body coulomb problem

A potential harmonic method that is suitable for the three-body coulomb systems is presented. This method is applied to solve the three-body Schroedinger equations for He and e ⁺ e ⁻ e ⁺ directly, and the calculations yield very good results for the energy. For example, we obtain a ground-state energy of −0.26181 hartrees for e ⁺ e ⁻ e ⁺, and −2.90300 hartrees for He with finite nuclear mass, in good agreement with the exact values of −0.26200 hartrees and −2.90330 hartrees. Compared with the full-set calculations, the errors in the total energy for ground and excited states of e ⁺ e ⁻ e ⁺ are very small, around −0.0001 hartrees. We conclude that the present method is one of the best PH methods for the three-body coulomb problem. Received: 5 September 1996 / Accepted: 14 July 1997     

Structural and thermodynamic characteristics of ionic associates in vapors over sodium bromide and iodide

Nonempirical methods are used to calculate the geometric parameters, the frequencies of normal vibrations, and thermochemical characteristics of ions existing in saturated vapors over sodium bromide and iodide: Na₂X⁺, NaX₂⁻, Na₃X₂⁺, and Na₂X₃⁻ (X = Br, I). According to the calculations, Na₂X⁺ and NaX₂⁻ triatomic ions have a linear equilibrium configuration of D _∞h symmetry. Pentaatomic ions can exist in the form of three isomers: linear with D _∞h symmetry, planar cyclic with C _2v symmetry, and bipyramidal with D _3h symmetry. At a temperature of ∼1000 K, Na₃X₂⁺ and NaX₃⁻ pentaatomic ions are shown to be present in vapor mainly in the form of linear isomers. The energies and enthalpies of ion molecular reactions with the participation of the above ions are calculated, and the formation enthalpies of the ions are determined, Δ _f H ^o(0 K): 293±2 kJ/mol (Na₂Br⁺), 354±2 kJ/mol (Na₂I⁺), −536±2 kJ/mol (NaBr₂⁻, −458±2 kJ/mol (NaI₂⁻, 24±5 kJ/mol (Na₃Br₂⁺, 143±5 kJ/mol (Na₃I₂⁺, −810±5 kJ/mol (Na₂Br₃⁻, and −675±5 kJ/mol (Na₂I₃⁻.