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.     

Determination of sulfite in beer samples using an amperometric fill and flow channel biosensor employing sulfite oxidase

A simple method is described to determine sulfite in beer samples using a fill and flow channel biosensor. A droplet of sample is placed into the inlet of a rectangular flow cell and begins to flow through the channel by capillarity. The flow is maintained and controlled by a porous outlet plug of defined porosity. In a rectangular flow cell, the sample solution flows through three consecutive zones: over a predictor electrode, an enzyme layer and a detector electrode. Together these three zones enable the differentiation between current due to sulfite and current due to other electroactive species in the sample. The predictor electrode is located upstream, and on the opposite channel wall to the enzyme layer and detector electrode, and is poised at the same potential (+0.65 V versus Ag/AgCl) as the detector electrode. On this electrode, the current contribution from all species in the sample solution that are oxidized at that potential is determined. The enzyme layer contains sulfite oxidase, which, in the process of oxidizing sulfite, produces hydrogen peroxide, which itself is reduced by excess sulfite. The current at the downstream detector electrode is therefore different from that at the predictor electrode as a result of the enzyme reaction and the difference of the currents, corrected for the dimensions of the electrodes, is proportional to the concentration of sulfite. The method enables a straightforward correction of the interfering current at the detector electrode and a determination of the analyte concentration. The effect of interferences from ascorbic acid, ethanol, sorbic acid and tartaric acid in the detection of sulfite is efficiently removed. The concentration of sulfite in a sample of beer measured by the biosensor is equivalent to that measured using a reference method based on the AOAC-recommended Monier-Williams method.     

Simultaneous determination of sulfite and phosphate in wine by means of immobilized enzyme reactions and amperometric detection in a flow-injection system

A flow-injection system is proposed for the simultaneous determination of sulfite and phosphate in wine. A sulfite oxidase immobilized reactor and purine nucleoside phosphorylase-xanthine oxidase co-immobilized reactor are incorporated at fixed positions (parallel configuration) in the flow line, which is based on the splitting of the flow after sample injection and subsequent confluence. A poly(1,2-diaminobenzene)-coated platinum electrode is used as an amperometric detector to detect selectively hydrogen peroxide generated enzymatically in the enzyme reactors, without any interference from oxidizable species and proteins present in wine. Because each channel has a different residence time, two peaks are obtained. The first peak corresponds to sulfite and the second peak to phosphate. The peak current is linearly related to the concentrations of sulfite between 1 × 10⁻⁵ and 2 × 10⁻³M and phosphate between 2 × 10⁻⁵ and 5 × 10⁻³M. The simultaneous determination of sulfite and phosphate in wine can be performed at a rate of 30 samples/hr with satisfactory precision (less than 1.2% RSD) and no pretreatment except for the sample dilution.     

Electrocatalytic sulfite biosensor with human sulfite oxidase co-immobilized with cytochrome c in a polyelectrolyte-containing multilayer

An efficient electrocatalytic biosensor for sulfite detection was developed by co-immobilizing sulfite oxidase and cytochrome c with polyaniline sulfonic acid in a layer-by-layer assembly. QCM, UV–Vis spectroscopy and cyclic voltammetry revealed increasing loading of electrochemically active protein with the formation of multilayers. The sensor operates reagentless at low working potential. A catalytic oxidation current was detected in the presence of sulfite at the modified gold electrode, polarized at +0.1 V (vs. Ag/AgCl 1 M KCl). The stability of the biosensor performance was characterized and optimized. A 17-bilayer electrode has a linear range between 1 and 60 μM sulfite with a sensitivity of 2.19 mA M⁻¹ sulfite and a response time of 2 min. The electrode retained a stable response for 3 days with a serial reproducibility of 3.8% and lost 20% of sensitivity after 5 days of operation. It is possible to store the sensor in a dry state for more than 2 months. The multilayer electrode was used for determination of sulfite in unspiked and spiked samples of red and white wine. The recovery and the specificity of the signals were evaluated for each sample. Figure Schematic of the bioelectrocatalytic sulfite sensor: sulfite oxidase (green) oxidizes sulfite to sulfate and transfers electrons via heme b ₅ to cyt c (red) and thence to the gold electrode     

Phosphate-sensitive enzyme electrode: a potential sensor for environment control

A highly sensitive enzyme electrode was designed for the assay of phosphate ions. For this purpose, a bienzyme membrane with co-immobilized nucleoside phosphorylase and xanthine oxidase was used with a platinum amperometric electrode for the detection of enzymatically generated hydrogen peroxide. A detection limit of 10^?7 M was obtained and phosphate assays could be easily performed in the range 0.1–10 μM, which is of interest in the control of water pollution.     

Determination of total sulfite in wine. Zone electrophoresis-isotachophoresis quantitation of sulfate on a chip after an in-sample oxidation of total sulfite

This work deals with the determination of total sulfite in wine. The determination combines an in-sample hydrogen peroxide oxidation of total sulfite in alkalized wine to sulfate with the separation and quantitation of the latter anion by zone electrophoresis (ZE) on-line coupled with isotachophoresis (ITP) on a column-coupling chip. Sample clean up, integrated into the ITP-ZE separation, eliminated wine matrix in an extent comparable to that provided by a highly selective distillation isolation of sulfite. At the same time, conductivity detection, employed to the detection of sulfate in the ZE stage of the ITP-ZE combination, provided for sulfate the concentration limit of detection corresponding to a 90 microg/l concentration of sulfite in the loaded sample (0.9 microl). Such a detectability allowed a reproducible quantitation of total sulfite when its concentration in wine was 15 mg/l. Formaldehyde binding of free sulfite in wine, included into the pre-column sample preparation, prevented an uncontrolled oxidation of this sulfite form. This step contributed to an unbiased determination of sulfate present in the original wine sample (this determination corrected for the concentration of sulfate determined in the sample after the peroxide oxidation of sulfite to the value equivalent to the total sulfite). The 99-101% recoveries of sulfite, determined for appropriately spiked wine samples, indicate a very good accuracy of the present method. Such a statement also supports excellent agreements of the results of quantitation based on the in-sample peroxide oxidation of the total sulfite (bound sulfite released at a high pH) with those in which this analyte was isolated from wine by distillation (bound sulfite released at a very low pH).     

Copper oxide nanoparticles and ionic liquid modified carbon electrode for the non-enzymatic electrochemical sensing of hydrogen peroxide

The direct electrocatalytic reduction of hydrogen peroxide in alkaline medium at a carbon ionic liquid electrode modified with copper oxide nanoparticles was investigated. The electrode was prepared by mixing graphite particles, ionic liquid (n-octylpyridium hexafluorophosphate) and copper oxide nanoparticles. Unlike the film-modified electrode, the fabrication of this electrode is simple and highly reproducible. The combination of the good conductivity of the ionic liquid and the high catalytic activity of the nanoparticles resulted in an electrode with attractive properties for the determination of hydrogen peroxide. The concentration of NaOH and the loading of copper oxide nanoparticles were optimized. The linear range for the determination of hydrogen peroxide is from 1.0 μM to 2.5 mM, the detection limit is 0.5 μM. High stability, sensitivity, selectivity and reproducibility, fast response, the ease of preparation, and surface renewal made the electrode well suitable for the determination of hydrogen peroxide in real samples.     

Optimization of two methods for the analysis of hydrogen peroxide: high performance liquid chromatography with fluorescence detection and high performance liquid chromatography with electrochemical detection in direct current mode

Two complementary methods were optimized for the separation and detection of trace levels of hydrogen peroxide. The first method utilized reversed-phase high-performance liquid chromatography with fluorescence detection (HPLC-FD). With this approach, hydrogen peroxide was detected based upon its participation in the hemin-catalyzed oxidation of p-hydroxyphenylacetic acid to yield the fluorescent dimer. The second method utilized high performance liquid chromatography with electrochemical detection (HPLC-ED). With this approach, hydrogen peroxide was detected based upon its oxidation at a gold working electrode at an applied potential of 400 mV vs. hydrogen reference electrode (Pd/H(2)). Both methods were linear across the range of 15-300 μM, and the electrochemical method was linear across a wider range of 7.4-15,000 μM. The limit of detection for hydrogen peroxide was 6 μM by HPLC/FD, and 0.6 μM by HPLC/ED. A series of organic peroxides and inorganic ions were evaluated for their potential to interfere with the detection of hydrogen peroxide. Studies investigating the recovery of hydrogen peroxide with three different extraction protocols were also performed. Post-blast debris from the detonation of a mixture of concentrated hydrogen peroxide with nitromethane was analyzed on both systems. Hydrogen peroxide residues were successfully detected on this post-blast debris.     

Influence of changes of platinum electrode surface condition on the kinetics of the oxidation of sodium dithionite and sulfite in alkaline solution

The influence of the surface condition of a platinum electrode on the kinetics of the electrochemical oxidation of sodium dithionite and sulfite was investigated. It was found that the oxidation of sulfite does only occur at platinum oxide while the oxidation of dithionite takes place at platinum oxide as well as at platinum hydroxide and bare platinum. However, dithionite cannot be oxidised at rearranged platinum hydroxide, which is formed during the reduction of platinum oxide, a process that is strongly dependent on the applied anodic vertex potential. For both substances a hysteresis effect was observed between forward and backward scan but in both cases the effects could be explained considering the platinum surface condition. As well in the absence as in the present of sulfite and/or dithionite reproducible current-potential curve were obtained after cycling three times between the applied vertex potentials. The observed difference between the first and subsequent scans again could be explained when the variation of the platinum surface condition as a function of potential and number of cycles was taken into consideration.     

Highly improved electrocatalytic behavior of sulfite at carbon ionic liquid electrode: application to the analysis of some real samples

The electrocatalytic oxidation of sulfite was investigated at carbon ionic liquid electrode (CILE). This electrode is a very good alternative to previously described electrodes because the electrocatalytic effect is achieved without any electrode modification. Comparative experiments were carried out using carbon paste electrode (CPE) and glassy carbon electrode (GCE). At CILE, highly reproducible and well-defined cyclic voltammograms were obtained for sulfite with a peak potential of 0.55 V vs. Ag/AgCl. Sulfite oxidation at CILE does not result in deactivation of the electrode surface. The kinetic parameters for this irreversible heterogeneous electron transfer process were determined. Under optimal experimental conditions, the peak current response increased linearly with sulfite concentration over the range of 6-1000 μM. The detection limit of the method was 4 μM. The method was applied to the determination of sulfite in mineral water, grape juice and non-alcoholic beer samples.     

Electrocatalytic Oxidation and Determination of Sulfite with a Novel Copper‐Cobalt Hexacyanoferrate Modified Carbon Paste Electrode

The electrocatalytic oxidation of sulfite has been studied at a stable electroactive thin film of copper‐cobalt hexacyanoferrate (CuCoHCF) hybrid electrodeposited on a carbon paste electrode (ECMCPE). A linear range of 5 μM to 5 mM of sulfite, with an experimental detection limit of 1 μM, was obtained using the cyclic voltammetric method. The oxidation of sulfite showed no significant fouling effect on the modified electrode surface at sulfite concentrations below 5 mM. The proposed modified electrode exhibited several attractive features, including simple preparation, fast response, good stability and repeatability, and could be applied to sulfite determination in real samples.     

Preparation of Pt/polypyrrole-ferrocene hydrogen peroxide sensitive electrode for the use as a biosensor

A polypyrrole electrode with ferrocene mediator is prepared and its sensitivity to hydrogen peroxide is investigated. The polypyrrole is deposited upon a 0.5 cm² Pt plate by the polymerization of pyrrole by scanning the electrode potential between 0.0 and 0.9 V at a scan rate of 50 mV/s. The platinum/polypyrrole-ferrocene (Pt/PPy-Fc) electrode is prepared by adding ferrocene to the coverage medium. The electrode’s sensitivity to hydrogen peroxide is investigated at room temperature using 0.025 M phosphate buffer at pH 7. The working potential is 0.7 V, the concentrations of pyrrole and ferrocene are 0.2 M and 10 mM. Polypyrrole was coated on the electrode surface within 26 cycles. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 2, pp. 160–164. The text was submitted by the authors in English.     

Electrocatalytic Reduction of H2O2 and Oxygen on the Surface of Thionin Incorporated onto MWCNTs Modified Glassy Carbon Electrode: Application to Glucose Detection

A new H₂O₂ enzymeless sensor has been fabricated by incorporation of thionin onto multiwall carbon nanotubes (MWCNTs) modified glassy carbon electrode. First 50 μL of acetone solution containing dispersed MWCNTs was pipetted onto the surface of GC electrode, then, after solvent evaporations, the MWCNTs modified GC electrode was immersed into an aqueous solution of thionin (electroless deposition) for a short period of time <5–50 s. The adsorbed thin film of thionin was found to facilitate the reduction of hydrogen peroxide in the absence of peroxidase enzyme. Also the modified electrode shows excellent catalytic activity for oxygen reduction at reduced overpotential. The rotating modified electrode shows excellent analytical performance for amperometric determination of hydrogen peroxide, at reduced overpotentials. Typical calibration at ?0.3 V vs. reference electrode, Ag/AgCl/3 M KCl, shows a detection limit of 0.38 μM, a sensitivity of 11.5 nA/μM and a liner range from 20 μM to 3.0 mM of hydrogen peroxide. The glucose biosensor was fabricated by covering a thin film of sol–gel composite containing glucose oxides on the surface of thionin/MWCNTs modified GC electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The detection limit, sensitivity and liner calibration rang were 1 μM, 18.3 μA/mM and 10 μM–6.0 mM, respectively. In addition biosensor can reach 90% of steady currents in about 3.0 s and interference effect of the electroactive existing species (ascorbic acid–uric acid and acetaminophen) is eliminated. The usefulness of biosensor for direct glucose quantification in human blood serum matrix is also discussed. This sensor can be used as an amperometric detector for monitoring oxidase based biosensors.     

Amperometric determination of sulfite using screen-printed electrodes modified with metallic nanoparticles

We report on the amperometric determination of sulfite using screen-printed carbon electrodes (SPCEs) modified with gold and silver nanoparticles that were deposited on the electrode to improve the capabilities of detection. The electrode is fairly selective and responds to sulfite with an oxidation current (at 300 mV and pH 6) in the 9.80 to 83.33 μM concentration range. The precision in terms of repeatability and reproducibility is 14.4 % and 10.7 % in the case of SPCEs modified by gold nanoparticles. The method was applied to the determination of sulfite in drinking water, pickle juice and vinegar. Recoveries ranged from 96 % to 104 %.

Lactate Biosensor Based on Hydrotalcite‐Like Compounds: Performances and Application to Serum Samples

A lactate biosensor based on lactate oxidase supported onto a hydrotalcite, electrochemically deposited on a platinum surface, was developed for the first time. For the best electrode configuration, a linear response up to 0.8 mM, with a limit of detection of 14 μM and a sensitivity of 91 mA M^?1 cm^?2, was obtained. The influence of some interferents due to the oxidation of hydrogen peroxide (at +0.35 V vs. SCE) was also studied. By controlling carefully the experimental conditions, the determination of lactate in a commercial serum sample in the presence of interferents was successfully accomplished.     

Flow Injection Amperometric Determination of Hydrogen Peroxide at Low Level in Aqueous Solution

Abstract

A method is proposed for the flow-injection amperometric determination of hydrogen peroxide. Iodine is generated, by injecting hydrogen peroxide solution into an eluent 0.2 M in potassium iodide and 1 Min sulphuric acid and 5×10^?3M in Mo(VI) and is monitored at a platinum electrode that is being held at 0.1 V versus SCE. the rectilinearity range is from 10^?3?10^?6 M and the method is simple, accurate and compared favourably with the titrimetric method involving starch as indicator.     

甲苯-乙醇介质中二茂铁催化分解过氧化氢机理的探讨

甲苯-乙醇介质中二茂铁催化分解过氧化氢机理的探讨;电子转移机理     

Electrocatalytic oxidation of sulfite by acetylferrocene at glassy carbon electrode

The electrochemical oxidation of sulfite catalyzed by acetylferrocene (AFc) at a glassy carbon electrode (GCE) in 0.2 M NaClO₄ aqueous solution has been studied by cyclic voltammetry. Although sulfite itself showed a sluggish electrochemical response at the GCE, the response could be enhanced greatly by using AFc as a mediator, which enables a sensitive determination of the substrate (sulfite). The reaction rate constant for catalytic oxidation was evaluated as (7.02 ± 0.05) × 10⁴ M ^?1 s^?1 by chronoamperometry. Experimental conditions that maximize the current efficiency of the electrocatalytic oxidation, such as the pH and both the catalyst (AFc) and substrate (sulfite) concentrations, were also investigated. The electrochemical kinetics of electrocatalytic oxidation of sulfite by AFc has been studied by cyclic voltammetry. In the presence of 5 × 10^?4 M AFc, the oxidation current is proportional to the sulfite concentration and the calibration plot was linear over the concentration range 2 × 10^?4–2.4 × 10^?3 M . This result can be applied in the determination of real samples. Copyright © 2005 John Wiley & Sons, Ltd.     

Fabrication of herbicide biosensors based on the inhibition of enzyme activity that catalyzes the scavenging of hydrogen peroxide in a thylakoid membrane.

A novel herbicide biosensor with a thylakoid modified membrane electrode is presented. Thylakoid, isolated from spinach leaves, was entrapped in a membrane of poly (vinylalcohol) with the styrylpyridinium group (PVA-SbQ). The thylakoid membrane was fixed on the surface of a platinum electrode. It was found that the enzymes in thylakoid kept their activity for several months in the membrane. The oxidative current of hydrogen peroxide in a Tris-HCl buffer solution (pH 7.4) was detected at the modified electrode by a differential pulse voltammetric method. In the presence of herbicides, the oxidation current from the hydrogen peroxide decreased due to an inhibitor effect on the enzymes in thylakoid compared with that in the absence of the herbicides. The changes in the oxidation current at the electrode were proportional to the herbicide concentrations. The sensor could be used to detect herbicides in concentration ranges of 3 x 10(-9) - 1.5 x 10(-7) M for paraquat, 1 x 10(-8) - 3 x 10(-7) M for diuron, 4 x 10(-8) - 3 x 10(-6) M for prometryn, 5 x 10(-8) - 5 x 10(-6) M for atrazine and 1 x 10(-7) - 5 x 10(-6) M for ametryn, respectively. The enzyme activity on scavenging hydrogen peroxide in the modified PVA-SbQ membrane was examined.     

Direct electrocatalytic reduction of hydrogen peroxide at a glassy carbon electrode modified with polypyrrole nanowires and platinum hollow nanospheres

A nonenzymatic sensor for hydrogen peroxide has been fabricated by dispersing platinum hollow nanospheres onto polypyrrole (PPy) nanowires to form a PPy-Pt hollow sphere nanocomposite on a glassy carbon electrode. The materials were characterized by transmission electron microscopy and scanning electron microscopy. The process and the sensor were characterized by electrochemical impedance spectroscopy, cyclic voltammetry, and chrono-amperometry and revealed that the electrode has a large electroactive surface area and small resistance to electron transfer. The linear range for the determination of hydrogen peroxide is from 3.5 µM to 9.9 mM, the detection limit is 1.2 µM (S/N?=?3), and the response time is 3 s. The electrode exhibited good stability and excellent repeatability.