A Multicommuted Flow‐based System for Hydrogen Peroxide Determination by Chemiluminescence Detection Using a Photodiode

Abstract

A simple, rapid, and automated assay for hydrogen peroxide in pharmaceutical samples was developed by combining the multicommutation system with a chemiluminescence (CL) detector. The detection was performed using a spiral flow‐cell reactor made from polyethylene tubing that was positioned in front of a photodiode. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. The chemiluminescence was based on the reaction of luminol with hydrogen peroxide catalyzed by hexacyanoferrate(III).

The feasibility of the flow system was ascertained by analyzing a set of pharmaceutical samples. A linear response within the range of 2.2–210 µmol l^?1 H₂O₂ with a LD of 1.8 µmol l^?1 H₂O₂ and coefficient of variations smaller than 0.8% for 1.0×10^?5 mol l^?1 and 6.8×10^?5 mol l^?1 hydrogen peroxide solutions (n=10) were obtained. Reagents consumption of 90 µg of luminol and 0.7 mg of hexacyanoferrate(III) per determination and sampling rate of 200 samples per hour were also achieved.     

Iridium(III) catalyzed oxidation of iodide ions in aqueous acidic medium

Oxidation of iodide ions by K₃Fe(CN)₆, catalyzed by hydrogen ions obtained from hydrochloric acid was found to be further catalyzed by iridium(III) chloride. Rate, when the reaction is catalyzed only by the hydrogen ions, was separated from the rate when iridium(III) and H⁺ions both, catalyze the reaction. Reactions studied separately in the presence as well as in the absence of IrCl₃ under similar conditions were found to follow second order kinetics with respect to [I⁻]. While the rate showed direct proportionality with respect to [K₃Fe(CN)₆] and [IrCl₃]. At low concentrations the reaction shows direct proportionality with respect to [H⁺] which tends to become proportional to the square of hydrogen ions at higher concentrations. Strong retarding affect of externally added hexacyanoferrate(II) ions was observed in the beginning but further addition affects the rate to a little extent. Changes in [Cl⁻] and also ionic strength of the medium have no effect on the rate. With the help of the intercept of catalyst graph, the extent of the reaction, which takes place without adding iridium(III), was calculated and was found to be in accordance with the values obtained from the separately studied reactions in which only H⁺ ions catalyze the reaction. It is proposed that iridium forms a complex, which slowly disproportionates into the rate-determining step. Thermodynamic parameters at four different temperatures were calculated.     

Mechanistic studies for modelling the metal ioncatalyzed tiron-hydrogen peroxide indicator reaction

Model building of kinetic-catalytic methods of determination is attempted for the tironhydrogen peroxide indicator reaction catalyzed by cobalt(II) and manganese(II) in alkaline medium. As a first approximation, rate equations for the metal ion-catalyzed reactions are derived from kinetic dependences on reagent concentrations and pH. More general models are obtained by considering the metal ion equilibria in the reaction mixture. For Co(II), a ternary tironhydrogen peroxideCo(II) complex was found to be responsible for the catalytic activity. As stability constants of peroxo (Co(II) complexes are unknown, only a qualitative approach can be given. Manganese catalyzes the indicator reaction in the presence of 1,10-phenanthroline or 2,2′-bipyridine. The initial rates under pseudo zero-order conditions in hydrogen peroxide and tiron correlate directly with the fraction of ternary activatortironMn(II) complex present. For bipyridine as activator, the rate constant is 1.31 × 10⁶ M^?1 min^?1 with respect to the ternary complex.     

Die durch Blei(II) und Kupfer(II) katalysierte Zersetzung von Wasserstoffperoxid als Endpunktindikation chelatometrischer Titrationen

Zusammenfassung Die Anwendung der durch Blei(II) und Kupfer(II) katalysierten Zersetzung von Wasserstoffperoxid als exotherme Indikatorreaktion bei katalytisch-thermometrischer Endpunktindikation chelatometrischer Bestimmungen wird gezeigt. Die katalytische Wirkung von Blei(II) wird in ammoniak-ammoniumtartrathaltiger Lösung (p_H 12) und die Wirkung von Kupfer(II) in ammoniumcarbonathaltigem (p_H 8,8), natriumhydroxid-natriumcarbonathaltigem (p_H 10) und in ammoniakalischem Medium herangezogen. Die direkte Titration von ÄDTA, DCTA und NTA mit Kupfer(II) und Blei(II), die inverse Titration dieser Metalle, wie auch die Bestimmung einiger Metallionen (Zn²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Pb²⁺, Bi³⁺, In³⁺, Th⁴⁺) durch Rücktitration wird beschrieben. Die genannten Ionen können im Milligramm- und Mikrogrammbereich mit befriedigender Genauigkeit bestimmt werden.

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The end-point indication of chelatometric titrations by the decomposition of hydrogen peroxide catalyzed by lead(II) and copper(II)

Summary The application of the decomposition of hydrogen peroxide as exothermic indicator reaction catalyzed by lead(II) and copper(II), to catalytic thermometric endpoint detection of chelatometric titrations is described. The catalytic action of lead(II) is applied in ammonia-ammonium tartrate solution (p_H 12), the action of copper(II) in ammonium carbonate (p_H 8.8), sodium hydroxide-sodium carbonate (p_H 10) and in ammoniacal medium (p_H 12). The direct titration of EDTA, DCTA and NTA with copper(II) and lead(II), the invers titration of this metals, as well as the determination of several ions (Zn²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Pb²⁺, Bi³⁺, In³⁺, Th⁴⁺) by backtitration has been developed. The ions mentioned can be determined in the milligram and in the microgram range with reasonable accuracy.

     

Determination of hydrogen peroxide by utilizing a cobalt(II)hexacyanoferrate-modified glassy carbon electrode as a chemical sensor

A mixed-valence cluster of cobalt(II)hexacyanoferrate possesses an electron transfer property and is suitable for the development of an effective hydrogen peroxide detection scheme. The characteristics of cobalt(II)hexacyanoferrate have been studied using both elemental analysis and infrared spectra, confirming the structure is Co[Fe^II(CN)₆]. The cobalt(II)hexacyanoferrate-modified electrode exhibits a rapid response (t_95% - 6.5 s) to the injection of 5.0 × 10⁻⁵ M hydrogen peroxide. The linearity of the response is up to 1.1 × 10⁻³ M (correlation coefficients is 0.999). The sensitivity of this modified electrode is 11.8 μA/mM-mm². The detection limit of cobalt(II)hexacyanoferrate-modified electrode to hydrogen peroxide is 6.25 × 10⁻⁸ M. The current chemical sensor modified with Co[Fe^II(CN)₆] has better sensitivity than previous ones. The modified glassy carbon electrode shows no interference from ascorbic acid, uric acid, acetaminophen, 1,4-dihydroxyquinone, dopamine at the 2.0 × 10⁻⁴ M level and polyamines at 5.0 × 10⁻⁵ M level.     

Microcalorimetric studies on the dismutation of superoxide anion catalyzed by superoxide dismutase

Ｓｕｐｅｒｏｘｉｄｅｄｉｓｍｕｔａｓｅ(ＳＯＤ,ＥＣ1.15.1.1),ｗｈｉｃｈｗａｓｆｏｕｎｄａｎｄｉｓｏｌａｔｅｄｆｒｏｍｂｏｖｉｎｅｅｒｙｔｈｒｏｃｙｔｅｓｂｙＭｃＣｏｒｄａｎｄＦｒｉｄｏｖｉｃｈｉｎ1969[1],ｉｓａｎｉｍｐｏｒｔａｎｔｍｅｍｂｅｒｏｆｔｈｅｆａｍｉｌｙｏｆｂｉｏｌｏｇｉｃａｌａｎｔｉｏｘｉｄａｎｔｓｔｒｅｓｓｅｎｚｙｍｅｓ.Ｔｈｉｓｅｎｚｙｍｅｈａｓｂｅｅｎｄｅｔｅｃｔｅｄｉｎａｗｉｄｅｒａｎｇｅｏｆｌｉｖｉｎｇｔｈｉｎｇｓａｎｄｈａｓｂｅｅｎｉｍｐｌｉｃａｔｅｄｉｎｔｈｅｉｎｔｅｒ…     

TS-1/H2O2碱溶液中低温氧化愈创木酚制备马来酸（英）

可再生生物质资源的开发与利用能够缓解化石燃料产生的温室气体对环境的负面影响.在生物质燃料制备过程中联产高附加值化学品能大幅提高生物质炼制的经济性.愈创木酚是常见的木质纤维素快速热解产物.本文研究了低温液相氧化愈创木酚制备马来酸,并重点考察了催化剂添加量、pH值、反应时间和反应温度等反应条件的影响.研究发现,在钛硅沸石-过氧化氢碱溶液氧化反应体系中（80℃,pH=13.3）,20₃0mol%的愈创木酚可以选择性转化为马来酸.同时初步探讨了愈创木酚氧化开环转化为马来酸的反应机理.     

Kinetics of hydrogen peroxide decomposition with complexed and “free” iron catalysts

The hydrogen peroxide decomposition kinetics were investigated for both “free” iron catalyst [Fe(II) and Fe(III)] and complexed iron catalyst [Fe(II) and Fe(III)] complexed with DTPA, EDTA, EGTA, and NTA as ligands (L). A kinetic model for free iron catalyst was derived assuming the formation of a reversible complex (Fe–HO₂), followed by an irreversible decomposition and using the pseudo‐steady‐state hypothesis (PSSH). This resulted in a first‐order rate at low H₂O₂ concentrations and a zero order rate at high H₂O₂ concentrations. The rate constants were determined using the method of initial rates of hydrogen peroxide decomposition. Complexed iron catalysts extend the region of significant activity to pH 2–10 vs. 2–4 for Fenton's reagent (free iron catalyst). A rate expression for Fe(III) complexes was derived using a mechanism similar to that of free iron, except that a L–Fe–HO₂ complex was reversibly formed, and subsequently decayed irreversibly into products. The pH plays a major role in the decomposition rate and was incorporated into the rate law by considering the metal complex specie, that is, EDTA–Fe–H, EDTA–Fe–(H₂O), EDTA–Fe–(OH), or EDTA–Fe–(OH)₂, as a separate complex with its unique kinetic coefficients. A model was then developed to describe the decomposition of H₂O₂ from pH 2–10 (initial rates = 1 × 10⁻⁴ to 1 × 10⁻⁷ M/s). In the neutral pH range (pH 6–9), the complexed iron catalyzed reactions still exhibited significant rates of reaction. At low pH, the Fe(II) was mostly uncomplexed and in the free form. The rate constants for the Fe(III)–L complexes are strongly dependent on the stability constant, K_ML, for the Fe(III)–L complex. The rates of reaction were in descending order NTA > EGTA > EDTA > DTPA, which are consistent with the respective log K_MLs for the Fe(III) complexes. Because the method of initial rates was used, the mechanism does not include the subsequent reactions, which may occur. For the complexed iron systems, the peroxide also attacks the chelating agent and by‐product‐complexing reactions occur. Accordingly, the model is valid only in the initial stages of reaction for the complexed system. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 24–35, 2000     

Kinetics and mechanism of ligand exchange of coordinated cyanide in hexacyanoferrate(II) by nitroso‐R‐salt in the presence of mercury(II) as a catalyst

The kinetics of Hg(II)‐catalyzed reaction between hexacyanoferrate(II) and nitroso‐R‐salt has been followed spectrophotometrically by monitoring the increase in absorbance at 720 nm, the λ_max of green complex, [Fe(CN)₅ N‐R‐salt]^3? as a function of pH, ionic strength, temperature, concentration of reactants, and the catalyst. In this reaction, the coordinated cyanide ion in hexacyanoferrate(II) gets replaced by incoming N‐R‐salt under the following specified reaction conditions: temperature = 25 ± 0.1°C, pH = 6.5 ± 0.2, and I = 0.1 M (KNO₃). The stoichiometry of the complex has been established as 1:1 by mole ratio method. The rate of catalyzed reaction is slow at low pH values and then increases with pH and attains a maximum value between 6.5 and 6.7. The rate finally falls again at higher pH values due to nonavailability of [H⁺] ions needed to regenerate the catalytic species. The rate of reaction increases initially with [N‐R‐salt] and attains a maximum value and then levels off at higher [N‐R‐salt]. The rate of reaction shows a variable order dependence in [Fe(CN)₆^4?] ranging from unity at lower concentration to 0.1 at higher concentrations. The effect of [Hg²⁺] on the reaction rate shows a complex behavior and the same has been explained in detail. The activation parameters for the catalyzed reactions have been evaluated. A most plausible mechanistic scheme has been proposed based on the experimental observations. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 222–232, 2005     

Homogeneous oxidation kinetics of aqueous ferrous iron at circumneutral pH

Oxidation of aqueous Fe(II) was investigated at circumneutral pH and 23°C in the absence of ligands (other than H₂O, OH^–, and Cl^–) and catalysts (e.g., microbes or solids surfaces). Enzymes (superoxide dismutase and catalase) were used as specific catalytic probes to determine whether superoxide and hydrogen peroxide are intermediates in oxygen reduction by Fe(II). The kinetic evidence suggests that Fe(II) and D.O. react in a termolecular transition state complex, the reaction produces hydrogen peroxide (probably without intermediation by superoxide), and Fe(II) and H₂O₂ react in a termolecular reaction or in a two-step sequence of bimolecular reactions. The rate data permit modeling the overall Fe(II) oxidation reaction at pH7.0 with a rate law that has non-integer orders with respect to [Fe(II)] and [OH^–].     

Chemiluminescent Determination of Vitamin B12 Using Charge Coupled Device (CCD)

A method was developed for the determination of vitamin B₁₂ based on the enhancement of cobalt (II) on the chemiluminescence (CL) reaction between luminol and percarbonate (powerful source of hydrogen peroxide). The release of cobalt (II) from the vitamin B₁₂ was reached by a simple and fast microwave digestion (20 s microwave digestion time and a mix of nitric acid and hydrogen peroxide). A charge coupled device (CCD) photodetector, directly connected to the cell, coupled with a simple continuous flow system was used to obtain the full spectral characteristics of cobalt (II) catalyzed luminol-percarbonate reaction.

The optima experimental conditions were established: 8.0 m mol L^?1 luminol in a 0.075 mol L^?1 carbonate buffer (pH 10.0) and 0.15 mol L^?1 sodium percarbonate, in addition to others experimental parameters as 0.33 mL s^?1 flow rate and 2 s integration time, were the experimental conditions which proportionate the optimum CL emission intensity. The emission data were best fitted with a second-order calibration graph over the cobalt (II) concentration range from 4.00 to 300 µ g L^?1 (r² = 0.9990), with a detection limit of 0.42 µ g L^?1. The proposed method was successfully applied to the determination of vitamin B₁₂ in pharmaceuticals.     

Reaction of hydrogen peroxide with low molecular weight iron complexes

Fe(II) complexed with trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) reacts with hydrogen peroxide in neutral aqueous solution at room temperature to yield reactive species which are not scavenged by t-butanol, under conditions where >90% of hydroxyl radical would be scavenged. Further, the ratio of the rate constants for the reaction of the reactive species with Fe(II)CDTA and H₂O₂ is 6.2, in contrast to a ratio of 200 which would result if the species were the hydroxyl radical. Thus, it is concluded that the reactive species produced is not the hydroxyl radical, but an iron-oxo species such as the ferryl ion. The reactive species is formed in an apparent first order reaction, when either hydrogen peroxide or Fe(II)CDTA is in kinetic excess. The bimolecular reaction rate constant is (1.26 ± 0.19) × 10³ M^-1 s^-1. In experiments where H₂O₂ was in kinetic excess, a chain decomposition of H₂O₂ was observed in which the initially produced iron-oxo intermediate exhibits hydroperoxidase activity.     

Direct Synthesis in the Undergraduate Laboratory: Synthesis of Copper Complexes from Zero-Valent Metals as a Demonstration of Base-Catalyzed Direct Synthesis

Direct synthesis is an important and active research field for scientists and technologists involved with the use of elemental metals. An undergraduate laboratory demonstration is presented that exposes students to this important synthetic technique. The direct synthesis of [Cu(NH₃)₄]²⁺ and [Cu(en)₂]²⁺ complexes in aqueous solution from zero-valent Cu metal is employed as an experiment illustrating the oxidizing properties of alkaline hydrogen peroxide solutions. The experiment also shows the decomposition of hydrogen peroxide catalyzed by the copper complexes. Finally, students can learn that the direct oxidation of metallic copper by alkaline hydrogen peroxide solution is an efficient and novel alternative approach to synthesize these and other copper complexes.     

Study and application of the complex of Sn(II) with glycerol in volumetric analysis

The preparation of standard Sn(II) solutions in glycerol and ethanol media was studied and the most suitable conditions were found for their standardization using dichromate and potassium hexacyanoferrate. Further, the long-term stability of standard Sn(II)-glyc solutions was studied and it was found that the titer of 0.1 N Sn(II)-glyc does not change in an inert atmosphere over a period of 4 months. The solution undergoes partial oxidation in the air (Fig. 1). It was demonstrated polarographically and voltammetrically that the studied redox system is irreversible. The formal redox potential value E_f⁰ = 0.80 V (SCE) 0.1 N Sn(II)-glyc can be back-titrated with 0.1 N K₂Cr₂O₇ in a sat. Na₂CO₃ solution under an inert atmosphere. Generally it is possible in sat. Na₂CO₃ medium to determine with great precision dichromate and potassium hexacyanoferrate, iodine, chloramine-T, chlorine lime, hydrogen peroxide, inorganic peroxides, and silver (Table 2). Equilibrium potentiometry, bipotentiometry, and biamperometry can be used for indication of the equivalence point.     

Kinetics and mechanism of hydrogen peroxide decomposition in the presence of the tetraaquapalladium(<Emphasis Type="SmallCaps">II</Emphasis>) complex

Kinetics of hydrogen peroxide decomposition in the presence of the tetraaquapalladium(II) complex in an aqueous solution at 40–70 °C was studied. The reaction rate is the first order with respect to the concentration of both Pd^II and H₂O₂ and the negative first order with respect to perchloric acid. Using free radicals traps, the reaction mechanism was found to differ from the traditional free-radical mechanism known for d-metal aqua ions and proceeds without generation of hydroxyl radicals. The kinetic data obtained suggest a mechanism involving the formation of an intermediate palladium complex with oxygen. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1077–1082, May, 2005.     

Determination of Hydrogen Peroxide Concentrations By Flow Injection Analysis Based On the Enhanced Chemiluminescent Reaction Using Peroxidase

Abstract

The technique of flow injection analysis was employed in the determination of hydrogen peroxide. the method was based on the chemiluminescence reaction of luminol with H₂O₂ which is catalyzed by horseradish peroxidase and enhanced by p-iodophenol. Hydrogen peroxide was linearly detected in the range 10^?6M-10^?4M by measuring the maximum intensity of light emitted. the detection limit is about 1 · 10^?6M hydrogen peroxide. Transition metal cations at millimolar concentrations do not have any interference on the determination of hydrogen peroxide by FIA based on the enhanced chemiluminescent reaction. This technique is relatively rapid and simple, and permits measurement of up to 80 samples/hr using generally available equipment.     

The dynamic behaviour of the silver-silver hexacyanoferrate(II) electrode: coulometric production of hexacyanoferrate(II)

The electrochemical behaviour of the silver-silver hexacyanoferrate(II) elec-trode was studied. The reaction Ag₄[Fe(CN)₆] + 4e^- → 4Ag + [Fe(CN)₆]^4- was shown to be useful for the coulometric production of hexacyanoferrate(II) ions in titrations of zinc(II). Coulometric titrations of organometallic compounds such as R₂Sn(ClO₄)₂, with electrically generated hexacyanoferrate(II) are also reported.     

Determination of pKa value, kinetic studies of decomposition and oxygen transfer for chromium(VI) peroxide

The determination of pK_a value for the unstable chromium(VI) peroxide, CrO(O₂)₂(H₂O) in aqueous solution is presented. The pK_a value is found to be (1.55 ± 0.03). The kinetic decomposition of chromium(VI) peroxide is dependent on the concentration of hydrogen peroxide in the pH range between 2.5 and 4.0. We have proposed the possible explanation for the formation of triperoxo chromium complex of hydrogen peroxide which is dependent on decomposition. Activation of coordinate peroxide in chromium(VI) peroxide observed in the kinetic studies is by reduction of thiolato-cobalt(III) complex. The rate constant (M⁻¹ s⁻¹, 15 °C) for the oxygen atom transfer reaction from CrO(O₂)₂(OH)⁻ to (en)₂Co(SCH₂CH₂NH₂)²⁺ is found to be (25.0 ± 1.3).     

Amperometric Determination of Galactose,Lactose and Dihydroxyacetone Using Galactose Oxidase in a Flow Injection System with Immobilized Enzyme Reactors and On-Line Dialysis

Abstract

A flow injection manifold containing a dialyzer and reactors with immobilized galactose oxidase and peroxidase was used for the determination of galactose in urine, lactose in milk and dihydroxyacetone in a biotechnological reaction medium. The hydrogen peroxide which is formed by the galactose oxidase reaction was detected by amperometric reduction of a mediator. The latter had been produced from hydrogen peroxide in a peroxidase catalyzed reaction. The hydrogen peroxide detection step was studied with several mediators and hexacyanoferrate (II) was selected. An ion exchange HPLC procedure was used to purify the galactose oxidase, in particular from catalase, and the kinetics and the selectivity of a reactor containing the immobilized enzyme was investigated. Columns for removal of certain interferents such as ascorbic acid were used in the determination of galactose in urine. The response to galactose standards was linear from the detection limit of 2 μM to 60 mM. The throughput was 45 samples per hour and the relative standard deviation 0.4%.