The effect of carbonyl complexation on highly exothermic vanadium oxidation reactions

The effects of CO complexation on highly exothermic vanadium oxidation reactions is evaluated. We study the chemiluminescent (CL) reaction products formed when vanadium vapor entrained in Ar or CO is oxidized by O₃ or NO₂. The multiple collision V+Ar+O₃→VO^*(C ⁴Σ⁻, ⁴Φ, ²X)+Ar+O₂ reactive encounter yields two previously unreported VO excited states, whereas the V+Ar+NO₂→VO^*+Ar+NO reactive encounter populates states up to and including VO^* C ⁴Σ⁻. The multiple collision V+nCO+O₃ reactive encounter would appear to form a VOCO excited state complex, emitting in the region 420–560 nm, via the formation and oxidation of V(CO)₂ viz. V(CO)₂+O₃→VOCO^*+CO+O₂ and a relaxed VO excited state emitter via V+nCO+O₃→VO^*+nCO+O₂ where the VO excited state excitation is mediated by V–CO complexation. In complement, the much less exothermic V–NO₂ encounter displays an emission which, in concert with previous studies of CO complexation, suggests the formation of a VO(CO)₂ excited state complex viz. V(CO)₂+NO₂→VO(CO)₂^*+NO. The experiments characterizing CL are complemented by comparative laser-induced fluorescence studies of the VO X ⁴Σ⁻–CO and Ar interactions and their influence on the VO C ⁴Σ⁻–X ⁴Σ⁻ laser-induced excitation spectrum. These studies, in conjunction with further attempts to excite LIF in the 420–560 nm region, suggest that the observed complex emissions result primarily from VO excited state interactions. Complementary time-of-flight mass spectroscopy of vanadium and vanadium-oxide–carbonyl complex formation demonstrates the formation of V(CO), V(CO)₂, V₂(CO), and VOCO, the latter three of which demonstrate clear metastable-ion dissociation peaks for the processes VOCO⁺→V⁺+CO₂, V(CO)₂⁺→V⁺+2CO, and V₂(CO)⁺→V₂⁺+CO, suggesting that these vanadium complexes when formed in a reaction-based environment may be photodissociated with light in the visible and ultraviolet regions.     

Determination of sulfur contents of SO3, S2O3 and S based on the electrocatalytic interaction with homogeneous mediator tris(2,2'-bipyridyl)Ru(II)

A sensitive voltammetric method has been developed for the determination of total or single species of sulfur anions containing sulfide, sulfite and thiosulfate. The method is based on the catalytic effect of tris(2,2'-bipyridyl)Ruthenium(II) (Ru(bpy)₂^+ 2) as a homogeneous mediator on the oxidation of those anions at the surface of a glassy carbon electrode. A reversible redox couple of Ru(II)/Ru(III) were observed as a solute in aqueous solution. Cyclic voltammetry study showed that the catalytic current of the system depends on the concentration of the anions. Optimum pH values for voltammetric determination of sulfite, thiosulfate and sulfide has been found to be 5.6, 10.0 and 10.0, respectively. Under the optimized conditions the calibration curves have been obtained linear in the concentration ranges of 0.8–500.0, 0.4–1000.0 and 0.5–5000.0 µmol L^− 1 of SO₃²⁻, S₂O₃²⁻ and S²⁻, respectively. The detection limits have been calculated to be 0.40, 0.17 and 0.33 µmol L^− 1 for SO₃²⁻, S₂O₃²⁻ and S²⁻, respectively. The diffusion coefficients of sulfite and thiosulfate have been estimated using chronoamperometry. The chronoamperometric method also has been used to determine the catalytic rate constant for catalytic reaction of the Ru(bpy)₂^+ 2 with sulfite and thiosulfate. Finally the proposed method has been used for the determination of total sulfur contents in real samples of water and wastewater. Moreover the sulfite content in sugar and sulfur dioxide in air has been determined with satisfactory results.     

Optimization of sample preparation using statistical methods: spectrophotometric determination of Fe and Co in pharmaceutical samples

This work presents alternatives for Fe and Co determination in pharmaceutical samples using flow analysis. The first procedure describes Fe extraction in mineral/vitamin complexes. The best conditions were reached when HNO₃ concentration and volume, sample mass and shaking time were 1.0 mol l⁻¹, 5 ml, 25 mg and 10 min. Three mineral/vitamin complexes of known concentrations (ranging from 12 to 32 g kg⁻¹) were analyzed (10 authentic replicates for each) and recoveries of around 100% were obtained when compared with a well-established mineralization procedure employing concentrated HNO₃ and H₂O₂ (30% w/v). The second work part shows the employment of Tiron and H₂O₂ reaction for Co determination in a drug for inappetence. The results (352±18.7 mg kg⁻¹) were compared with those using Electrothermal Atomic Absorption Spectrometry—ETAAS (346±15.7 mg kg⁻¹). The proposed method showed detection and quantification limits of 0.20 and 0.70 μg l⁻¹, respectively. Both procedures for Fe and Co determination presented time, reagent and effort reduction.     

Three-way principal component analysis of chemical data from Lake Como watershed

A large data set obtained by a one-year monthly determination of ions (F⁻, Cl⁻, Br⁻, NO₃⁻, NO₂⁻, PO₄³⁻, SO₄²⁻, Na⁺, K⁺, Ca²⁺, Mg²⁺, NH₄⁺) and trace metals of environmental concern (Ni, Co, Mn, Fe) from the tributaries of Lake Como (Lombardy, Northern Italy) was treated by three-way Principal Component Analysis. The results showed that the chemical features of the investigated rivers are mainly related to the lithology of the watershed. Some cases of contamination were evidenced and rationalized on the basis of anthropic pollution or on the basis of the geochemical features of the territory. The method here proposed allows an easy and quick interpretation of the chemical data by means of graphical devices. The information extracted by the three-way models would be very useful to regional agencies in developing a strategy to manage water resources in the whole basin of Lake Como.     

Development of an integrated flow injection system for the electro-oxidative leaching of uranium from geological samples and its spectrophotometric determination with Arsenazo III

This work proposes a new procedure for on-line electro-oxidative leaching and spectrophotometric determination of uranium in ore samples. By associating a conventional flow injection system, used for uranium determination with Arsenazo III, with an on-line system for electro-oxidative leaching, a fully integrated system was assembled. The systems were integrated after achieving optimum conditions for uranium determination and leaching. According to the results obtained in the present work, a current density of 280 mA cm⁻² generated enough hypochlorite ions in the electrolyte solution (3.6 mol L⁻¹ HCl + 2% (w/v) NaCl) to promote quantitative oxidation of U(IV) to U(VI) thus improving the extraction efficiency. The slurry density did not significantly affect the performance of the system and the increasing temperature resulted in a decrease in extraction efficiency. This methodology was applied in the determination of U₃O₈ in four ore samples and the results obtained agreed with those obtained by ICP-MS after conventional wet acid digestion of the samples.     

Chemiluminescence in O2 oxidation of organosodium compounds of polycyclic aromatic hydrocarbons and benzophenone

Chemiluminescence (CL) in oxidation of organosodium compounds by O₂ in THF was studied. Emitters of CL are excited complexes of polycyclic aromatic hydrocarbons, excimers¹(R·R)^*. The mechanism of their formation was proposed. The Na⁺, R^.−+O₂ CL system is a unique source for the selective generation of excimers of aromatic hydrocarbons. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 284–288, February, 1997.     

Highly sensitive determination of hydroxylamine using fused gold nanoparticles immobilized on sol-gel film modified gold electrode

We are reporting the highly sensitive determination of hydroxylamine (HA) using 2-mercapto-4-methyl-5-thiazoleacetic acid (TAA) capped fused spherical gold nanoparticles (AuNPs) modified Au electrode. The fused TAA-AuNPs were immobilized on (3-mercaptopropyl)-trimethoxysilane (MPTS) sol-gel film, which was pre-assembled on Au electrode. The immobilization of fused TAA-AuNPs on MPTS sol-gel film was confirmed by UV-vis absorption spectroscopy and atomic force microscopy (AFM). The AFM image showed that the AuNPs retained the fused spherical morphology after immobilized on sol-gel film. The fused TAA-AuNPs on MPTS modified Au electrode were used for the determination of HA in phosphate buffer (PB) solution (pH = 7.2). When compared to bare Au electrode, the fused AuNPs modified electrode not only shifted the oxidation potential of HA towards less positive potential but also enhanced its oxidation peak current. Further, the oxidation of HA was highly stable at fused AuNPs modified electrode. Using amperometric method, determination of 17.5 nM HA was achieved for the first time. Further, the current response of HA increases linearly while increasing its concentration from 17.5 nM to 22 mM and a detection limit was found to be 0.39 nM (S/N = 3). The present modified electrode was also successfully used for the determination of 17.5 nM HA in the presence of 200-fold excess of common interferents such as urea, NO₂⁻, NH₄⁺, oxalate, Mn²⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺ and Cu²⁺. The practical application of the present modified electrode was demonstrated by measuring the concentration of HA in ground water samples.     

Voltammetry and electrochemical stripping analysis for antimony in aqueous and nonaqueous media after extraction

Cyclic voltammetry of antimony was studied in aqueous media (HCl-LiCl) and in nonaqueous media after extraction with 20% tri-n-butylphosphate in toluene, with a rotating glassy carbon disc electrode. Reduction of antimony to the element in aqueous media is nearly reversible, but irreversible in nonaqueous media. Anodic stripping voltammetric and chronopotentiometric determinations were also studied in nonaqueous media; methanol and LiCI, NH₄SCN or NH₄NO₃, were used as base electrolytes. In nonaqueous media, antimony can be determined down to concentrations of 1O⁻⁸ M by stripping voltammetry, and lO⁻⁷ M by stripping chronopotentiometry. Electrochemical stripping determinations of 10⁻⁶ M antimony(III) were not affected by Co²⁺, Ni²⁺, Cd²⁺, Zn²⁺ or As³⁺ (5 · 10⁻³ M), ag⁺ (4 · 10⁺⁴ M in stripping voltammetry or 10⁻³ M in stripping chronopotentiometry), Hg²⁺ (5 · 10⁻⁴M), Pb²⁺ (3 · 10⁻⁴ M), Cu²⁺ (1.5 · 10⁻⁴ M)Sn²⁺ and Sn⁴⁺ (7 · 10⁻⁴ M), Fe³⁺ (4 · 10⁻⁴ M), Au³⁺ (5 · 10⁻⁵ M) and Bi³⁺ (1.5 · 10⁻⁵ M). Thestripping chronopotentiometric determination showed better selectivity.     

Synthesis of glass ceramics containing finely dispersed particles of aluminum-doped M-type strontium hexaferrite

Glasses with nominal compositions SrFe₁₀Al₂O₁₉+4(SrB₂O₄+Sr₂B₂O₅) (1) and SrFe₉Al₃O₁₉+4(SrB₂O₄+Sr₂B₂O₅) (2) were prepared by rapid quenching of melts. Thermal treatment of glass samples at 600–900 °C resulted in crystallization of the magnetic phase SrFe_12−x Al_xO₁₉ (x = 1.1±0.1) and strontium borates. Platelet hexaferrite particles with average sizes from (250×60) nm² to (450×140) nm² were prepared. The coercive force of glass ceramics is 580 and 475 kA m⁻¹ for glasses 1 and 2, respectively. The coercive force of 580 kA m⁻¹ is the highest known value compared to hexaferrite particles prepared earlier by glass crystallization.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 74–77, January, 2005.     

A1 → E emission of 1-phosphapropyne cation, CH3CP

The ²A₁ → ²E emission spectrum of CH₃CP⁺ in the gas phase has been observed in the 530–590 nm region. The cations were produced by electron impact on either an effusive beam or seeded helium supersonic free jet or CH₃CP. Two pairs of spin-orbit separated bands are identified: O⁰₀, ^O_O and 2^O₁, ^O₁. The derived constants are (in cm⁻¹): T₀=18656(1), a″_O=−85(2) and ν″₂=1503(2).     

A new generation of cyanide ion-selective membranes for flow injection application: Part III. A simple approach to the determination of toxic metal-cyanide complexes without preliminary separation

A new flow injection approach to total weak acid-dissociable (WAD) metal–cyanide complexes is proposed, which eliminates the need of a separation step (such as gas diffusion or pervaporation) prior to the detection. The cornerstone of the new methodology is based on the highly selective flow-injection potentiometric detection (FIPD) system that makes use of thin-layer electroplated silver chalcogenide ion-selective membranes of non-trivial composition and surface morphology: Ag_2 + δSe_1 − xTe_x and Ag_2 + δSe. An inherent feature of the FIP-detectors is their specific response to the sum of simple CN⁻ + Zn(CN)₄²⁻ + Cd(CN)₄²⁻. For total WAD cyanide determination, ligand exchange (LE) and a newly developed electrochemical pre-treatment procedure for release of the bound cyanide were used. The LE pre-treatment ensures complete recovery only when the sample does not contain Hg(CN)₄²⁻. This limitation is overcome by implementing electrochemical pre-treatment which liberates completely the bound WAD cyanide through cathodic reduction of the complexed metal ions. A complete recovery of toxic WAD cyanide is achieved in the concentration range from 156 μg L⁻¹ up to 13 mg L⁻¹. A three-step protocol for individual and group WAD cyanide speciation is proposed for the first time. The speciation protocol comprises three successive measurements: (i) of non-treated, (ii) LE-exchange pre-treated; (iii) electrochemically pre-treated sample. In the presence of all WAD complexes this procedure provides complete recovery of the total bound cyanide along with its quantitative differentiation into the following groups: (1) Hg(CN)₄²⁻; (2) CN⁻ + Cd(CN)₄²⁻ + Zn(CN)₄²⁻; (3) Cu(CN)₄³⁻ + Ni(CN)₄²⁻ + Ag(CN)₂⁻. The presence of a 100-fold excess in total of the following ions: CO₃²⁻, SCN⁻, NH₄⁺, SO₄²⁻ and Cl⁻ does not interferes. Thus the proposed approach offers a step ahead to meeting the ever increasing demand for cyanide-species-specific methods. The equipment simplicity makes the procedure a good candidate for implementing in portable devices for in-field cyanide monitoring.     

A study on terbium sensitized chemiluminescence of ciprofloxacin and its application

A novel rapid flow injection method with chemiluminescence (CL) detection was established for the determination of ciprofloxacin (CPLX), which is an antibiotic commonly used. The method is based on CL of Ce(IV)–SO₃²⁻ sensitized by Tb³⁺–CPLX, and showed the intensive bands characteristic of Tb³⁺ (⁵D₄→⁷F₅). The optimum conditions for CL emission were investigated. The linear relationship between the relative CL intensity and the concentration of CPLX is in the range of 9.0×10⁻⁹–1.0×10⁻⁶ mol/l with a detection limit of 3.1×10⁻¹⁰ mol/l. The relative standard deviation is 2.8% (n=11) for a level of 5.0×10⁻⁸ mol/l. The method was applied to the analysis of CPLX in human serum and urine samples with satisfactory results. The possible mechanism for this sensitized CL reaction is also discussed.     

Microdetermination of Proteins with the 1,10-Phenanthroline–H2O2–Cetyltrimethylammonium Bromide–Cu(II) Chemiluminescence System

Proteins can enhance the chemiluminescence (CL) intensity of the 1,10-phenanthroline–H₂O₂–cetyltrimethylammonium bromide (CTMAB)–Cu(II) system because unsaturated complexes of Cu(II) with protein have a much stronger catalytic effect on the CL reaction than does Cu(II). On this basis, a new flow injection analysis method for detection of some proteins was established. The method gives linear responses over two orders of magnitude and detection limits at the 0.02–0.05 μg ml⁻¹level for bovine serum albumin, human serum albumin, γ-globulin, and egg albumin. The method was used for determination of proteins in human serum with satisfactory results.     

Reactions of small negative ions with O2(a Δg) and O2(X Σg)

The rate constants and product ion branching ratios were measured for the reactions of various small negative ions with O₂(X ³Σ_g⁻) and O₂(a ¹Δ_g) in a selected ion flow tube (SIFT). Only NH₂⁻ and CH₃O⁻ were found to react with O₂(X) and both reactions were slow. CH₃O⁻ reacted by hydride transfer, both with and without electron detachment. NH₂⁻ formed both OH⁻, as observed previously, and O₂⁻, the latter via endothermic charge transfer. A temperature study revealed a negative temperature dependence for the former channel and Arrhenius behavior for the endothermic channel, resulting in an overall rate constant with a minimum at 500 K. SF₆⁻, SF₄⁻, SO₃⁻ and CO₃⁻ were found to react with O₂(a ¹Δ_g) with rate constants less than 10⁻¹¹ cm³ s⁻¹. NH₂⁻ reacted rapidly with O₂(a ¹Δ_g) by charge transfer. The reactions of HO₂⁻ and SO₂⁻ proceeded moderately with competition between Penning detachment and charge transfer. SO₂⁻ produced a SO₄⁻ cluster product in 2% of reactions and HO₂⁻ produced O₃⁻ in 13% of the reactions. CH₃O⁻ proceeded essentially at the collision rate by hydride transfer, again both with and without electron detachment. These results show that charge transfer to O₂(a ¹Δ_g) occurs readily if the there are no restrictions on the ion beyond the reaction thermodynamics. The SO₂⁻ and HO₂⁻ reactions with O₂(a) are the only known reactions involving Penning detachment besides the reaction with O₂⁻ studied previously [R.S. Berry, Phys. Chem. Chem. Phys., 7 (2005) 289–290].     

Bifunctional sensor of nitric oxide and oxygen based on hematite nanotubes embedded in chitosan matrix

A novel hybrid bifunctional sensing platform for simultaneous determination of NO and O₂ has been developed, whereby hematite nanotubes are immobilized into the chitosan matrix onto a gold electrode (labeled as HeNTs-Chi/Au). The HeNTs distributed in porous-structured chitosan matrix not only offer abundant active sites for bifunctional sensing of NO and O₂, but also facilitate oxidation of NO and reduction of O₂ dramatically. Straight calibration curves are achieved in analyte concentration ranges of 5.0 × 10⁻⁸ to 1.25 × 10⁻⁶ mol L⁻¹ for NO and 2.5 × 10⁻⁷ to 6.0 × 10⁻⁶ mol L⁻¹ for O₂. Also, the detection limits are low of 8.0 × 10⁻⁹ mol L⁻¹ for NO and 5.0 × 10⁻⁸ mol L⁻¹ for O₂. Such an efficient bifunctional sensor for NO and O₂ offers great potential in quantitation of NO levels in biological and medical systems, since NO level is highly regulated by various reactive oxygen species.     

Structural studies in main group chemistry : XXII. Structural and tin-119 mössbauer studies of some five-coordinate triorganotin anions

The structures of two complexes, [Ph₃PCH₂Ph]⁺[Bu₃SnCl₂⁻]⁻ and [Ph₃AsCH₂COPh]⁺[Ph₃SnCl₂]⁻, have been determined by X-ray diffraction. Both materials are monoclinic, space group P2_1/c. Unit cell data for [Ph₃PCH₂Ph]⁺−[Bu₃SnCl₂]⁻ are a 9.8521(6), b 16.9142(4), c 22.3517(7) Å, β 91.4235(9)°; and for [Ph₃AsCH₂COPh]⁺[Ph₃SnCl₂]⁻ a 34.9760(3), b 11.1290(5), c 24.2410(2) Å, β 108.56(2)°, and both consist of the component ionic species. The organotin anions each have trigonal bipyramidal geometry with equatorial organic groups and axial halogens. In the [Ph₃SnCl₂]⁻ anion the two Sn---Cl bond distances are the same (2.58(1) and 2.60(1) Å), but in [Bu₃SnCl₂]⁻, as in [Me₃SnCl₂]⁻, they are substantially different (2.573(7) and 2.689(6) Å). The Sn---C bond distances also vary: [Ph₃SnCl₂]⁻ 2.15(4), 2.16(3) and 2.25(5); [Bu₃SnCl₂]⁻ 2.21(1), 2.20(2) and 2.29(2) Å. Tin-119 Mössbauer data for these and several other similar complexes are also reported.     

Kinetics and mechanisms of the catalyzed decomposition of hydrogen peroxide by ethylenebis(oxyethylenedinitrilo)tetracetate complex of iron(III)

The rate of decomposition of H₂O₂ in the presence of Fe(III)-y complex (y is ethylenebis(oxyethylenedinitrilo)tetraacetic acid (EGTA) anion) was investigated under variable conditions of pH and temperature, various water-miscible solvents, and different concentrations of H₂O₂, [Fe-y]⁻, and acetate ions. The following rate law holds: Rate = (k₁K₃K₄/[H⁺]) [Fe-y(OH)]²⁻ [H₂O₂] at pH less than 9.80, and Rate = (k₂K₅[H⁺]/K₃) [Fe-y(OH)₂]³⁻[OOH]⁻ at pH above 9.80. The values of k₁K₄and k₂K₅ at 25 °C were found to be 1523 and 0.747 M⁻¹ S⁻¹, respectively. Activation enthalpy and activation entropy for this reaction were determined from Arrhenius plots and found to be ΔH^* = 34.38 K J mol⁻¹ and ΔS^* = −167.2 J K⁻¹ mol⁻¹.     

A Spectroscopic Study of the Dissolution of Cesium Phosphomolybdate and Zirconium Molybdate by Ammonium Carbamate

Through a combination of Raman spectroscopy, multi-element NMR spectroscopy and chemical analysis, the differences between the action of carbonate and carbamate as agents for dissolving Cs₃PMo₁₂O₄₀⋅xH₂O(s) (CPM) and ZrMO₂O₇(OH)₂(H₂O)₂(s) (ZM) have been elucidated. Alkaline H₂NCO⁻₂/HCO₃⁻/CO₃²⁻ solutions, derived from the dissolution of ammonium carbamate (NH₄H₂NCO₂; AC), dissolve CPM by base hydrolysis of the PMo₁₂O₄₀³⁻ Keggin anion, ultimately forming [MoO₄]²⁻ and PO₄³⁻ when excess base is present. If the initial concentration of H₂NCO₂⁻/HCO₃⁻/ CO₃²⁻ is lowered, base hydrolysis is incomplete and the dissolved species include [Mo₇O₂₄]⁶⁻ and [P₂Mo₅O₂₃]⁶⁻, and undissolved solid Cs₃PMo₁₂O₄₀, Cs_xNH_7−xPMo₁₁O₃₉, and Cs_xNH_6−xMo₇O₂₄ remain. Na₂CO₃ solutions dissolve Cs₃PMo₁₂O₄₀ through a similar mechanism, but the dissolution rate is much lower. We attribute this difference to the different buffering effects of H₂NCO₂⁻/HCO₃⁻/CO₃²⁻ and CO₃²⁻/HCO₃⁻ solutions, and the instability of carbamic acid, the protonated form of H₂NCO₂⁻ (which rapidly decomposes into NH₃ and CO₂). The ability of NH₃ to produce NH₄⁺ and OH⁻, together with the evolution of CO₂ gas, drive the reaction forward. Low temperature measurements under conditions where pure H₂NCO₂⁻ is kinetically stable, allowed the rates of dissolution of CPM by H₂NCO₂⁻ and CO₃²⁻ to be compared directly, confirming the faster dissolution by H₂NCO₂⁻. Compared to CPM, the dissolution of ZM by H₂NCO₂⁻/HCO₃⁻/CO₃²⁻ is a much slower process and is driven by the formation of soluble Zr^IV-carbonate complexes and MoO₄²⁻. The driving force for the dissolution of ZM is the superior complexing ability of carbonate over carbamate; consequently solutions containing a higher carbonate concentration dissolve ZM faster.     

Stratospheric chemical ionization mass spectrometry: nitric acid detection by different ion molecule reaction schemes

Detailed height profiles of stratospheric nitric acid mixing ratios have been derived with a baloon borne chemical ionization mass spectrometer by applying several ion molecule reaction schemes, each associated to a specific and selective ion source. These ions (CO₃⁻, Cl_n⁻, CF₃O⁻, and CF₃O⁻H₂O) give rise to specific product ions (mainly CO₃⁻HNO₃, NO₃⁻HCl, NO₃⁻HF, and CF₃O⁻HNO₃) upon reaction with ambient nitric acid molecules. This paper reports on the instrumental details as well as on the results obtained during two balloon flights with the instrument. Within the accuracy of the measurements, the nitric acid height profiles obtained with the three different ion sources are in good agreement with one another as well as with literature data.