A tr esr study of the reactions of excited organic triplet molecules with inorganic sulfur oxoanions

The reactions of excited triplet ketones including benzophenone, 4,4′-dihydroxybenzophenone, and acetone with inorganic sulfur oxoanions: sulfite (SO₃ ⁼), metabisulfite (S₂O₅ ⁼), and dithionite (S₂O₄ ⁼) in solution were studied by TRESR. Observation of radical anion intermediates polarized by the Triplet Mechanism demonstrated the reactions of electron transfer from the sulfur dianions to the organic triplet states. Thus, electron transfer from SO₃ ⁼ to the triplet organic carbonyl compounds gave rise to the SO₃ ^? radical; reactions with metabisulfite and dithionite were more complex and may be interpreted as occurring via electron transfer to the carbonyl system followed by dissociation of the S-S bond in the resulting sulfur oxoanion radical. The initial radical ion pairs thus formed consist of pairs of anion radicals, one organic and one inorganic.     

Capillary electrophoretic determination of thiosulfate,sulfide and sulfite using in-capillary derivatization with iodine

A new capillary electrophoresis (CE) method was developed for the rapid, simple and selective determination of thiosulfate, sulfide and sulfite species. The proposed method is based on the in-capillary derivatization of separated sulfur anions by mixing their zones with the iodine zone during the electrophoretic migration and direct UV detection of iodide formed. The optimal conditions for the separation and derivatization reaction were established by varying electrolyte pH, electrolyte counter-ion, concentration of iodine, and applied voltage. The optimized separations were carried out in 20 mmol/L Tris-chloride electrolyte (pH 8.5) using direct UV detection at 214 nm. All three sulfur species were well resolved in less than 4 min. The method gives repeatability comparable or even better than this obtained for sulfur anions using standard CE technique. The proposed CE system was applied to the monitoring of sulfur anions in spent fixing solutions during the electrolytic oxidation.     

Electrochemical determination of sulfide and sulfite ions by pneumatoamperometry

Sulfide and sulfite ions in aqueous solution are converted through acidification to hydrogen sulfide and sulfur dioxide, which are purged from solution with nitrogen carrier gas. The volatile species are detected through oxidation in 1 M sulfuric acid at an anodically polarized platinum electrode separated from the gas stream by a gas-permeable polymer membrane. Mixtures of sulfide and sulfite are separated and determined independently through pH control during acidification. Interferences from metal ions, which form sulfide precipitates, and other anions, which form volatile species on acidification, are discussed.     

Electroanalytical Chemistry of Sulfur Compounds For the New Coal Conversion Technologies

Abstract

Polarographic methods are described “tailor-made” for the speciation and determination of sulfur contaminants in synfuels and coal gasification/liquefaction process streams. In samples containing the anions, S^2? _x, sulfidic sulfur was quantitated by anodic depolarization of the dropping mercury electrode, while polysulfidic sulfur was determined with the aid of an electroreduction process implicating 2(x-1) electrons. Polythionates were electroreduced to thiosulfate, sulfite, sulfide and/or mixtures thereof, under judiciously controlled experimental conditions. Thiosulfate and sulfite were quantitated by differential pulse polarography at dropping mercury anodes via reactions involving formation of thiosulfato- and sulfitomercurates.     

Determination of sulfur-containing inorganic anions by dual ion chromatography and capillary electrophoresis – application to the characterization of bacterial sulfur degradation

An analytical characterization of microbiological oxidation and reduction of sulfur anions has been performed with dual ion chromatography. The apparatus consisted of two chromatographic lines combined by a sample injection valve that allows the simultaneous introduction of a sample solution to both systems. With system 1 non-suppressed conductivity detection of sulfite and sulfate after separation in phthalate eluent was performed. For sulfide, thiosulfate and thiocyanate amperometric detection using a carbonate eluent was carried out on system 2. Parallel runs were possible for these species which could not be separated with one system. Optimizing separation and detection, limits of quantification of 0.02–0.3 mg/L could be obtained. The on-line coupling of a reaction vial to the injection valve was used to investigate the bacterial conversions, because the samples could be taken without contamination and air introduction. Thiosulfate was detected as a metabolite in both sulfur reduction and oxidation. Capillary electrophoresis with conductivity detection was applied as a complimentary technique for monitoring the bacterial sulfur oxidation. The results showed good correlation to the concentration values obtained by ion chromatography.     

Determination of sulfur-containing inorganic anions by dual ion chromatography and capillary electrophoresis – application to the characterization of bacterial sulfur degradation

An analytical characterization of microbiological oxidation and reduction of sulfur anions has been performed with dual ion chromatography. The apparatus consisted of two chromatographic lines combined by a sample injection valve that allows the simultaneous introduction of a sample solution to both systems. With system 1 non-suppressed conductivity detection of sulfite and sulfate after separation in phthalate eluent was performed. For sulfide, thiosulfate and thiocyanate amperometric detection using a carbonate eluent was carried out on system 2. Parallel runs were possible for these species which could not be separated with one system. Optimizing separation and detection, limits of quantification of 0.02–0.3 mg/L could be obtained. The on-line coupling of a reaction vial to the injection valve was used to investigate the bacterial conversions, because the samples could be taken without contamination and air introduction. Thiosulfate was detected as a metabolite in both sulfur reduction and oxidation. Capillary electrophoresis with conductivity detection was applied as a complimentary technique for monitoring the bacterial sulfur oxidation. The results showed good correlation to the concentration values obtained by ion chromatography. Received: 14 May 1999 / Revised: 7 July 1999 / Accepted: 10 July 1999     

Riboflavin-sensitized photochemical radical ion chain reaction of sulfo-group substitution for halogen in halogenated hydroxynaphthalenes

It was shown that riboflavin (RF) is a sensitizer for the radical ion chain reaction of sulfo group substitution for halogen in halogenated hydroxynaphthalenes. The initaition mechanism involves the electron transfer reaction between the sulfite ion and excited riboflavin. The quantum yields of RF radical anions from the singlet and the triplet states upon excitation in an aqueous sodium sulfite solution are 0.01 and 0.15, respectively, as determined by means of flash photolysis. The principal decay reaction for RF radical anions is their recombination with sulfite radical anions in the bulk of solution at a rate constant of (3.8 ± 0.5) × 10⁹ dm³ mol^?1 s^?1. The quantum yields of the riboflavin-sensitized substitution reaction increases in the presence of electron scavengers (chloranil, dinitrobenzene) and inorganic salts in the system.     

Photoreactions of p-quinones with dimethyl sulfide and dimethyl sulfoxide in aqueous acetonitrile. goerner@mpi-muelheim.mpg.de

The effects of dimethyl sulfide (DMS) and dimethyl sulfoxide (DMSO) on the photoreactions of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 9,10-anthraquinone (AQ) and several derivatives in acetonitrile/water were studied. The observed triplet state of the quinones is quenched and the rate constant is close to the diffusion-controlled limit for reactions of most quinones with DMS and lower with DMSO. Semiquinone radical anions (Q*-) produced by electron transfer from sulfur to the triplet quinone were detected. For both DMS and DMSO the yield of Q*- is similar, being generally low for BQ and NQ, substantial for AQ and largest for chloranil. The specific quencher concentrations and the effects of quinone structure and redox potentials on the time-resolved photochemical properties are discussed.     

Mechanism and reaction rate of the karl-fischer titration reaction: Part III. Rotating ring-disk electrode measurements— comparison with the aqueous system

A platinum disk-platinum ring electrode was used to investigate the oxidation of sulfur dioxide by iodine and triiodide in aqueous solutions. Contrary to methanolic solutions, where the monomethyl sulfite ion is the only oxidizable species, in aqueous solutions both the hydrogen sulfite ion and the sulfite ion can be oxidized. The reaction rate was generally so high, that the method for measurements of homogeneous second order reactions had to be used. At pH values >5, the reaction proceeded too fast to be measured reliably. In a solution “diluted” with ethanol (50% of weight), however, the reaction rate was within the range where a rotating ring-disk electrode can be applied to measure fast homogeneous reactions. At very low pH values both the first order calculation technique and the second order method could be used. The results with both methods were in fair agreement.     

NMR and EPR studies of the reaction of nucleophilic addition of (bi)sulfite to the nitrone spin trap DMPO

The reaction of the nitrone spin trap 5,5‐dimethylpyrroline‐N‐oxide (DMPO) with sodium (bi)sulfite in aqueous solutions was investigated using NMR and EPR techniques. Reversible nucleophilic addition of (bi)sulfite anions to the double bond of DMPO was observed, resulting in the formation of the hydroxylamine derivative 1‐hydroxy‐5,5‐dimethylpyrrolidine‐2‐sulfonic acid, with characteristic ¹H and ¹³C NMR spectra. The reaction mechanism was suggested and corresponding equilibrium constants determined. The mild oxidation of the hydroxylamine results in the formation of an EPR‐detected spectrum identical with that for the DMPO adduct with sulfur trioxide anion radical. The latter demonstrates that a non‐radical addition reaction of (bi)sulfite with DMPO may contribute to the EPR detection of SO₃^?? radical. This possibility must be taken into account in spin trapping analysis of sulfite radical. Copyright © 2003 John Wiley & Sons, Ltd.     

Radiation-Stimulated Oxidation Reactions of Oxo Anions in Aqueous Solutions

The common features of oxidation processes for inorganic oxo anions under the action of ionizing radiation are considered. The radiation-stimulated oxidation reactions of lower nitrogen, phosphorus, arsenic, and sulfur oxo anions occur via a chain mechanism. The kinetics of these processes can be explained in terms of the peroxide oxidation theory. A correlation between the kinetic and thermodynamic characteristics of the assumed rate-determining step is observed, thus proving the uniformity of oxidation mechanisms. Ways to use the processes of interest in practice are proposed.     

The salt effect on riboflavin-photosensitized substitution of the sulfo group for bromine in 1-bromo-2-hydroxynaphthalene

It was shown that the substitution reaction of the sulfo group for bromine in 1-bromo-2-hydroxynaphthalene photosensitized with riboflavin occurred via the riboflavin triplet state. Electron-donor anions quench the fluorescence of riboflavin. Halide (iodide and bromide) ions increase the quantum yield of the substitution reaction at low concentrations because of an increase in the spin-orbital coupling in the radical ion pair generated in riboflavin fluorescence quenching. As a result of the spin-orbital conversion, the triplet-state radical ion pair is formed, which separates into the riboflavin radical anion and the halogen atom. The halogen atom is reduced by the sulfite ions with the simultaneous formation of the sulfite radical anions, which participate in the propagation of the substitution reaction chain. All salts increase the quantum yield of the substitution reaction at high concentrations (>0.5 mol l^?1).     

Sulfur speciation by capillary zone electrophoresis: conditions for sulfite stabilization and determination in the presence of sulfate, thiosulfate and peroxodisulfate

Capillary zone electrophoresis (CZE) was used for the separation of the sulfur species SO3(2-), SO4(2-), S2O(3-) and S2O8(2-). Using an electrolyte system with 9.5 mmol L(-1) potassium chromate as UV-absorbing probe and 1 mmol L(-1) diethylenetriamine (DETA) as electroosmotic flow modifier, various possibilities for the stabilization of sulfite and electrophoretic separation of the sulfur anions were investigated. By adding 5% propanol as a stabilizer to both the working electrolyte and the sample solution, a good stabilization for sulfite and a separation of the sulfur anions in a short analysis time (4 min) was achieved. The advantages by using propanol instead of other stabilizers often used in analytical techniques are discussed. The electrophoretic separation of the sulfur anions was optimized with respect to the pH of the working electrolyte and concentration of the electroosmotic flow modifier (DETA). The detection limits achieved for SO3(2-), SO4(2-), S2O3(2-) and S2O8(2-) were 0.35, 0.25, 0.78 and 0.80 mg L(-1), respectively.     

Towards high capacity latex-coated porous polymer monoliths as ion-exchange stationary phases

The preparation of high capacity agglomerated monolithic ion-exchangers for capillary ion chromatography is described. Post-modification of reactive monoliths was investigated as an alternative to co-polymerisation of a suitable functional monomer with an overarching goal of increasing ion-exchange capacity. Direct sulfonation of poly styrene-co-divinyl benzene monoliths using concentrated sulfuric acid or chlorosulfonic acid was unsuccessful even for monoliths containing as low as 8% crosslinker. In contrast, chemical transformation of reactive monoliths containing glycidyl methacrylate was used to increase the ion-exchange capacity by up to more than thirty-fold with ion exchange capacities of 14-29 microequiv g(-1) achieved. Three different reactions were considered, including reaction with 4-hydroxybenenesulfonic acid under basic conditions; reaction with thiobenzoic acid followed by transformation to a reactive thiol and the subsequent oxidation to the sulfonic acid; and direct sulfonation with sodium sulfite. Of these, the reaction with sodium sulfite resulted in the most significant increase in the capacity and the best separation performance. In the isocratic mode separation efficiencies of over 13,500 plates m(-1) were observed (for iodate). The separation of seven inorganic anions was also demonstrated using a hydroxide gradient.     

Quantitative determination of sulfur-containing anions in complex matrices with capillary electrophoresis and conductivity detection.

The analysis of sulfur species in complex matrices, like environmentally related samples, requires selective and sensitive as well as robust determination methods. As many as possible different anions need to be quantified in a reasonable analysis time. Besides ion chromatography, capillary electrophoresis has proven to be a very efficient technique for the separation and determination of ionic compounds. With the advantages of less sample and solvent consumption compared to conventional LC, short separation time, inexpensive and robust capillaries, CE was used to separate the anions sulfate, sulfite, thiosulfate, thiocyanate and sulfide. Detection and injection modes and the composition of the separation buffers have been varied to find the most suitable conditions. Conductivity detection after electrokinetic sample injection and improvement of calibration linearity allowed the determination of sulfur containing anions with low limits of detection (8 to 50 micrograms/l). The developed CE method was applied to the analysis of water from an open-pit mining lake.     

Stabilization of sulfide and sulfite and ion-pair chromatography of mixtures of sulfide, sulfite, sulfate and thiosulfate

Ion chromatography of sulfide, sulfite, sulfate and thiosulfate in a mixture is often difficult because of instability of sulfide and sulfite, poor separation of sulfide from common anions such as bromide or nitrate and similar elution-times for sulfite and sulfate. An ion-pair chromatographic method for the determination of these sulfur anions has been established by stoichiometric conversion of sulfide and sulfite into stable thiocyanate and sulfate, respectively, prior to the chromatographic run. Sulfate, thiosulfate and thiocyanate were resolved on an octadecylsilica column with an acetonitrile-water mobile phase containing tetrapropylammonium salt (TPA) as an ion-paring reagent, and thiosulfate and thiocyanate in the effluent could be measured with a photometric detector (220 nm) and sulfate with a suppressed conductivity detector. When an acetonitrile-water (6:94, v/v) mobile phase (pH 5.0) containing 15 mM TPA and small amounts of acetic acid was used at a flow-rate of 0.6 ml min(-1), the three anions could be eluted within 32 min. Calibration plots of peak height versus concentration for sulfide (detected as thiocyanate) and thiosulfate gave straight lines up to 35 and 60 microM, respectively. The calibration plot for sulfide coincided with that obtained by using thiocyanate. A calibration plot for sulfite, measured as sulfate, was also linear up to 135 microM and was in accord with that of sulfate. Each calibration plot gave a correlation coefficient greater than 0.999. For six replicates obtained for a mixture of 30.0 microM sulfide, 50.0 microM sulfite, 50.0 microM sulfate and 20.0 microM thiosulfate, the proposed method gave a mean value of 30.1 microM with a standard deviation (SD) of 0.77 microM and a relative standard deviation (RSD) of 2.6% for sulfide, 101 microM (SD = 3.5 microM, RSD = 3.5%) for the total of sulfite and sulfate and 20.1 microM (SD = 0.44 microM, RSD = 2.2%) for thiosulfate. Recoveries for sulfide, sulfite plus sulfate, and thiosulfate in hot-spring water samples using the proposed method were found to be quantitative.     

SO2在多组分悬浮液中的吸收反应特性

The emission of sulfur dioxide in flue gases is an important problem in industry involving combustion of coal. The wet scrubbing process using lime/limestone slurry as the scrubbing medium is currently the dominant technology for the flue gas desulfurization. Due to the presence of numerous ionic and neutral species in the slurry, the chemical reactions involved in the slurry upon absorption of sulfur dioxide are complex. In this paper, a method of measuring the sulfur dioxide absorption in multi-component suspensions was developed and the characteristics of sulfur dioxide absorption were investigated. The results show that different additives chosed in the experiment can improve the ability of SO2 absorption. As to the same additive, the improvement effect is differ with different concentration. For the magnesium hydroxide additive, its optimum concentration is 1×10-4 mol/L. Experiment results suggested that dissolved sulfur dioxide reacts mainly with the magnesium sulfite ion pair which is responsible for the increased absorption rate of SO2. However, when CO2-3 or SO24- anions are present in the solution, the catalytic effect of magnesium hydroxide precipitate on sulfur dioxide absorption reduces. According to the experiments, absorbents with better performance can be optimized to be applied in semi-dry or wet FGD process to raise SO2 removal efficiency.     

High performance liquid chromatographic determination of bound sulfide and sulfite and thiosulfate at their low levels in human serum by pre-column fluorescence derivatization with monobromobimane.

A sensitive and specific high performance liquid chromatographic method for the determination of sulfide, sulfite, and thiosulfate was established. Inorganic sulfur anions were converted into fluorescent derivatives with monobromobimane. The derivatives were separated on a coupled column chromatography with a reversed-phase octadecyl silica column connected with a weakly basic anion exchanger column by isocratic elution with acetic acid solution (pH 3)-acetonitrile (13:3, v/v) containing 25 mM NaClO4. The method was applied to the determination of bound sulfide and sulfite and thiosulfate in normal human serum. Thiosulfate could be determined directly by use of an ultrafiltered sample. For the determination of bound sulfide and sulfite, the pretreatment step with continuous flow gas dialysis was effective for the sample after releasing sulfide and sulfite by reduction with dithiothreitol. The limits of quantification by the present method were 0.05 microM for thiosulfate, 0.5 microM for bound sulfide, and 0.2 microM for bound sulfite.     

Electrochemical Sensor for Sulfite and Sulfur Dioxide Based on 3‐Aminopropyltrimethoxysilane Derived Sol‐Gel Composite Electrode

A new sol‐gel derived composite sensor has been developed for the determination of sulfite and sulfur dioxide using 3‐aminopropyltrimethoxysilane, ferrous sulfate and graphite powder by sol‐gel process. Cyclic voltammetry and amperometry studies revealed that the modified iron dispersed sol‐gel derived ceramic composite electrode exhibited excellent characteristics for the electrocatalytic oxidation of sulfite at a reduced potential of +0.35 V with good sensitivity and selectivity. The pH and the potential for sulfite estimation have been optimized. The sensor exhibited rapid and linear response to sulfite in the concentration range from 0.73 mg/L to 95.42 mg/L with a correlation coefficient of 0.997. The proposed sensor can be utilized for the determination sulfur dioxide after absorbing in a suitable medium and has promising characteristics such as, rapid response, good reproducibility and remarkable stability.     

A novel preparation of cyclic sulfites through photosulfoxidation of alkenes

The cyclic sulfite, 4-ethyl-5-methyl-1,3,2-dioxathiolane 2-oxide, has been prepared by the photosulfoxidation of trans-2-pentene, and the quantum yield for the reaction has been determined. The proposed mechanism involves the reaction of a charge transfer complex formed between sulfur dioxide and the alkene, and is consistent with the participation of the triplet state of the former.