Hydrogen peroxide monitoring

The formation and decay of the compound l-type ferryl intermediate in the reaction of 150 jjiM tryptophan 2.3-dioxygenase with 900 xM hydrogen peroxide monitored by EPR spectroscopy at 10 K. (a) Seven representative EPR spectra (traces A to G) are shown in a 2D plot for the reaction of 0,12,30,60,90,240, and 600 s in the parallel samples, (b) The high spin EPR signal of TDO (A), H2O2 treated TDO at 30 s (B). 

The earliest examples of analytical methods based on chemical kinetics, which date from the late nineteenth century, took advantage of the catalytic activity of enzymes. Typically, the enzyme was added to a solution containing a suitable substrate, and the reaction between the two was monitored for a fixed time. The enzyme s activity was determined by measuring the amount of substrate that had reacted. Enzymes also were used in procedures for the quantitative analysis of hydrogen peroxide and carbohydrates. The application of catalytic reactions continued in the first half of the twentieth century, and developments included the use of nonenzymatic catalysts, noncatalytic reactions, and differences in reaction rates when analyzing samples with several analytes. 

The Reich test is used to estimate sulfur dioxide content of a gas by measuring the volume of gas required to decolorize a standard iodine solution (274). Equipment has been developed commercially for continuous monitoring of stack gas by measuring the near-ultraviolet absorption bands of sulfur dioxide (275—277). The deterrnination of sulfur dioxide in food is conducted by distilling the sulfur dioxide from the acidulated sample into a solution of hydrogen peroxide, foUowed by acidimetric titration of the sulfuric acid thus produced (278). Analytical methods for sulfur dioxide have been reviewed (279). 

The reaction in equation 55 occurs when there is insufficient hydrogen peroxide reductant in the absorber solution. Monitoring of the hydrogen peroxide concentration is important because is unstable in strong alkaline solutions, decomposing to water and oxygen. A small excess of sodium hydroxide is... 

It is possible to monitor the reaction and determine the end point by the absence of an a,/S-unsaturated ketone absorption in the UV or by the determination of the consumption of ca. one molar equivalent of hydrogen peroxide by permanganate titration. 

Preparing tert-butyl peroxide by the effect of 50% hydrogen peroxide in the presence of 78% sulphuric acid has led to numerous accidents. They were due to the high exothermicity of the reaction causing a temperature rise and leading to the explosive decomposition of the peroxide formed, if the temperature rise is badly monitored. 

The parameter most commonly monitored in this research is the extent of hydrogen peroxide decomposition. Measurement of tensile strength and/or the degree of polymerisation can be useful indicators of fibre damage. The effect of iron(III) ion concentration in accelerating the rate of peroxide decomposition is shown in Figure 10.23,... 

Figure 15.9 The results of capture ELISA on native RNase A and formalin-treated RNase A. Right panel, native RNase A (curve 1) and unfractionated formalin-treated RNase A (curve 2). Left panel, individual fractions of formalin-treated RNase A monomer (curve 3), dimmer (curve 4), trimer (curve 5), tetramer (curve 6), and a mixture of oligomers with >5 cross-linked proteins (curve 7). The ELISA plate wells were coated with monoclonal antibody against bovine pancreatic RNase A (1 pg/mL) overnight at 4°C and then blocked with bovine serum albumin. The wells were incubated for lh at 37°C in the presence of various concentrations of antigen in lOOpL of PBS. After washing, each plate well received a 1 4000 dilution of horseradish peroxidase conjugated rabbit polyclonal anti-RNase A antibody followed by incubation at ambient temperature for lh. After washing, detection was achieved using a mixture of 2,2,-azino-di-(3-ethylbenzthiazoline-6-sulphonate) and hydrogen peroxide. Absorbance was monitored at 405 nm. See Rait etal.11 for details.

XOD is one of the most complex flavoproteins and is composed of two identical and catalytically independent subunits each subunit contains one molybdenium center, two iron sulfur centers, and flavine adenine dinucleotide. The enzyme activity is due to a complicated interaction of FAD, molybdenium, iron, and labile sulfur moieties at or near the active site [260], It can be used to detect xanthine and hypoxanthine by immobilizing xanthine oxidase on a glassy carbon paste electrode [261], The elements are based on the chronoamperometric monitoring of the current that occurs due to the oxidation of the hydrogen peroxide which liberates during the enzymatic reaction. The biosensor showed linear dependence in the concentration range between 5.0 X 10 7 and 4.0 X 10-5M for xanthine and 2.0 X 10 5 and 8.0 X 10 5M for hypoxanthine, respectively. The detection limit values were estimated as 1.0 X 10 7 M for xanthine and 5.3 X 10-6M for hypoxanthine, respectively. Li used DNA to embed xanthine oxidase and obtained the electrochemical response of FAD and molybdenum center of xanthine oxidase [262], Moreover, the enzyme keeps its native catalytic activity to hypoxanthine in the DNA film. So the biosensor for hypoxanthine can be based on... 

The flow-cell design was introduced by Stieg and Nieman [166] in 1978 for analytical uses of CL. Burguera and Townshend [167] used the CL emission produced by the oxidation of alkylamines by benzoyl peroxide to determine aliphatic secondary and tertiary amines in chloroform or acetone. They tested various coiled flow cells for monitoring the CL emission produced by the cobalt-catalyzed oxidation of luminol by hydrogen peroxide and the fluorescein-sensitized oxidation of sulfide by sodium hypochlorite [168], Rule and Seitz [169] reported one of the first applications of flow injection analysis (FTA) in the CL detection of peroxide with luminol in the presence of a copper ion catalyst. They... 

Various hydroxyl and amino derivatives of aromatic compounds are oxidized by peroxidases in the presence of hydrogen peroxide, yielding neutral or cation free radicals. Thus the phenacetin metabolites p-phenetidine (4-ethoxyaniline) and acetaminophen (TV-acetyl-p-aminophenol) were oxidized by LPO or HRP into the 4-ethoxyaniline cation radical and neutral V-acetyl-4-aminophenoxyl radical, respectively [198,199]. In both cases free radicals were detected by using fast-flow ESR spectroscopy. Catechols, Dopa methyl ester (dihydrox-yphenylalanine methyl ester), and 6-hydroxy-Dopa (trihydroxyphenylalanine) were oxidized by LPO mainly to o-semiquinone free radicals [200]. Another catechol derivative adrenaline (epinephrine) was oxidized into adrenochrome in the reaction catalyzed by HRP [201], This reaction can proceed in the absence of hydrogen peroxide and accompanied by oxygen consumption. It was proposed that the oxidation of adrenaline was mediated by superoxide. HRP and LPO catalyzed the oxidation of Trolox C (an analog of a-tocopherol) into phenoxyl radical [202]. The formation of phenoxyl radicals was monitored by ESR spectroscopy, and the rate constants for the reaction of Compounds II with Trolox C were determined (Table 22.1). 

When bleaching wood pulp in a paper mill, the amount of leftover or residual hydrogen peroxide present in the spent bleach liquor can be important. Sometimes the bleach liquor is used in a second bleach or recycled back to the first bleach. Also, the residual peroxide level can indicate whether the bleach liquor makeup needs adjusting. Laboratory scale bleach tests are performed on the wood pulp, and the residual peroxide levels are checked by titration of the spent bleach liquors using potassium iodide and sodium thiosulfate. By monitoring the residual peroxide levels of these bleaches, the bleach liquor makeup can be adjusted, giving the best level, as needed by each paper mill. 

Iodide ion-selective electrode The iodide electrode has broad application both in the direct determination of iodide ions present in various media as well as for the determination of iodide in various compounds. It is, for example, important in the determination of iodide in milk [44,64,218, 382, 442], This electrode responds to Hg ions [150, 306, 439] and can be used for the indirect determination of oxidizing agents that react with iodide, such as 10 [305], lOi [158], Pd(II) [117, 347,405] and for the determination of the overall oxidant content, for example in the atmosphere [393], It can also be used to monitor the iodide concentration formed during the reactions of iodide with hydrogen peroxide or perborate, catalyzed by molybdenum, tungsten or vanadium ions, permitting determination of traces of these metals [12,192,193, 194, 195]. The permeability of bilayer lipid membranes for iodide can be measured using an I"... 

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