Detection and Inhibition of an Organic Interference in the Indigo Method for Ozone

Abstract

Aqueous samples of organic solutes often exhibit a delayed reaction in the indigo test for dissolved ozone which is similar to the reaction of ozone itself. This phenomenon has made timing critical in aqueous ozone measurements and has been observed in both laboratory situations with high organic carbon:ozone ratios and in a potable water treatment plant with low organic carbon:ozone ratios. Organic hydroperoxides, singlet oxygen, and Fenton's reagent but not triplet oxygen, hydrogen peroxide, nor p-benzoquinone were found to interfere. Addition of phenolic antioxidants was found to inhibit the interference. These results extend the utility of the indigo method to solutions of high organic carbon concentration.     

Determination of Bismuth by Adsorptive Stripping Voltammetry Using Aluminum Oxide for Elimination of Environmental Sample Matrix Interferences

The aim of this work was to find a fast new and simple method for efficient elimination of negative influence of humic substances and synthetic surfactants in the voltammetric determination of bismuth. The negative influence of the organic matrix present in environmental water samples due to their adsorption on aluminum oxide was successfully evaluated. The organic compounds such as humic substances and surface active compounds were removed by adsorption on the surface of aluminum oxide from the water samples. The application of this method was the recovery of Bi(III) from spiked water samples.     

Effective UV photolytic decomposition of organic compounds with a low-pressure mercury lamp as pretreatment for voltammetric analysis of trace metals

The effectivity of UV irradiation with low and high pressure mercury (L-Hg and H-Hg) lamps on the decomposition of organic compounds in aqueous solutions, as pretreatment for the voltammetric determination of trace metals, is compared. The photolytic decomposition with the L-Hg lamp was much faster than with the H-Hg lamp. The higher efficiency of the L-Hg lamp is caused by its greater light intensity at short wavelengths. Interferences of organic compounds on the voltammetric determination of nickel and indium were eliminated successfully by 90 min irradiation with the L-Hg lamp. Humic acid and organic interference with the voltammetric determination of nickel in natural river water were successfully eliminated. The decomposition using the L-Hg lamp can be carried out without added oxidizing reagents and at room temperature, thus eliminating loss of water samples by evaporation at higher temperature.     

Determination of mercury in aquatic ecosystems

Small concentrations of mercury are determined by the example of the quantitative recovery of a toxicant from snow water in a segregating system with no organic solvent (water-antipyrine-sulfosalicic acid). The organic component of the system in situ forming as a result of acid-base interactions was used in microliter amounts to modify a graphite indicator electrode and register an analytical signal of mercury. The reliability of the results of voltammetric determination was checked by the independent cold vapor method. Organic components obtained by segregation were used to extract mercury from the conservative ecosystem component, solid snow particles, snow water preconcentrated with a membrane filter, river suspensions from surface water and floodplain soils, and also fish samples. The characteristic features of mercury extraction with a mixture if mineral acids and the liquid organic component of a segregating system with no organic solvent are discussed.     

Effect of chlorination and ozone pre-oxidation on the photobacteria acute toxicity for dissolved organic matter from sewage treatment plants

The effect of chlorination and ozone pre-oxidation on the photobacteria acute toxicity for dissolved organic matter (DOM) from sewage treatment plants was investigated in this study. The results show that ozone pre-oxidation enhanced the photobacteria acute toxicity of the water samples. DOM before and after ozone pre-oxidation was fractionated by resins into six kinds of hydrophobic and hydrophilic organics. The six fractions were chlorinated individually and the photobacteria acute toxicity before and after chlorination was tested. It was found that the percentage of hydrophilic organics in DOM significantly increased after ozone pre-oxidation and hydrophilic organics exhibited remarkably higher acute toxicity than hydrophobic organics. In view of potentiometric titration and fourier transform infrared (FTIR) analysis, the hydrophilic organics showed a rather higher content of ph-OH structures than hydrophobic organics.     

氯化和臭氧预氧化处理对污水中溶解性有机物发光细菌急性毒性的影响

考察了氯化和臭氧预氧化对污水中DOM 的发光细菌急性毒性的影响. 结果表 明, 臭氧预氧化处理后发光细菌的急性毒性显著增强. 利用树脂吸附将臭氧预氧化前后 的DOM 分离为疏水性和亲水性等6 种组分, 对DOM 的6 种组分分别氯化, 考察了氯化 前后各组分的发光细菌急性毒性. 结果发现, 亲水性组分的比例在臭氧预氧化后明显增 加, 且亲水性有机物的急性毒性显著强于疏水性有机物. 结合电位滴定和傅立叶红外分 析发现, 与疏水性有机物相比, 亲水性有机物具有较高含量的ph-OH 官能团.     

Theoretical analysis of physicochemical processes occurring during water treatment by ozone and ultraviolet radiation

The paper presents a kinetic model developed for ozone dissolution in water and taking into account convective and diffusion processes occurring in the vicinity of floating bubbles that contain an ozone-air mixture. It was shown that the gradient of ozone concentration in a convective-diffusion layer and consequently the rate of ozone transfer from bubbles to the solution depended on the rate of ozone decomposition both in its reaction with organic admixtures and in the conditions of exposure to ultraviolet radiation. The obtained kinetic curves of destruction of organic compounds and changes of ozone concentration in water and ozone-air mixture are compared with experimental data for humic acids. The paper also analyzes additional factors affecting the kinetics of ozone dissolution and the rate of resultant reactions.     

Application of a Carbon Paste Electrode Modified with a Schiff Base Ligand to Mercury Speciation in Water

A carbon paste electrode, modified with benzylbisthiosemicarbazone is used for mercury speciation in water samples. Mercury ion is selectively accumulated on the electrode surface at open circuit and its analysis was performed by cyclic voltammetry or square‐wave voltammetry (SWV). A detection limit of 8 μg L^?1 (3σ) was found for 15 min of accumulation using SWV as measurement technique. The effect of several metallic ions and organic substances on voltammetric signal is examined. For speciation purposes, a ligand competition methodology between ligands in solution and electrode is used. Model mercury complexes are characterized as a function of their dissociation kinetics. The method was applied to mercury speciation in water samples from the Jarama River in Madrid.     

Simple and Highly Selective Catalytic Adsorptive Voltammetric Method for Cr(VI) Determination

A simple and highly selective and sensitive catalytic adsorptive stripping voltammetric procedure for determination of traces of Cr(VI) in the presence of a large excess of Cr(III) in environmental water samples is reported. To obtain a low detection limit the voltammetric procedure of chromium determination in the presence of DTPA and nitrate was exploited. For elimination of interference of Cr(III) ethylenediaminedisuccinic acid was used as a masking agent. At optimized conditions the calibration graph is linear from 2×10^?10 to 2×10^?8 mol L^?1 for accumulation time of 30 s. The validation of the procedure was performed by comparison of the results of analysis of river water samples with those obtained using other accepted voltammetric procedure.     

The oxidative destruction of lignin in the ozonation of wood

The oxidative destruction of lignin in the ozonation of aspen wood was studied. The kinetic curves of ozone consumption for samples with different contents of water were obtained. The consumption of ozone increased as the content of water grew. The second derivatives of the UV absorption spectra of lignin were obtained to show that the principal direction of lignin transformations under the action of ozone was the destruction of its aromatic constituents with the formation of carboxyl- and carbonyl-containing compounds. Measurements of the UV diffuse reflectance and EPR spectra of wood showed that the ozonation of wood caused the destruction of lignin quinoid structures. Part of lignin remained unchanged under the action of ozone. A key role in the destruction of wood lignin was played by ozone dissolved in water. Varying the content of water in wood samples allows various lignin transformation products to be obtained through ozonation.     

Ceramic membranes for ozonation in wastewater treatment

Ozone, due to its high oxidative capacity, is often used in water treatment for the degradation of organic pollutants. Unfortunately, the application of ozone in the form of gas bubbles causes foam problems. To avoid the development and accumulation of foam, the transfer of ozone into the water through gas permeable membranes was investigated. Ceramic membranes were used because of the chemical inertness of the material. The hydrophilic behaviour of ceramic membranes made of metal oxides causes the water to penetrate into the pores. This creates a diffusion resistance for the ozone which decreases the transfer rates. To keep the water out of the porous structure and maintain the gas/water interface at the membrane surface, the surface properties of the membrane were changed. The membrane was soaked in a solution of a fluorinated compound. Water drop measurements and transfer rates were investigated and confirmed the stability of the hydrophobic nature of the membrane surface. The ozone transfer rates thus achieved were in the range of 12 grams of ozone per square meter per hour.     

Selective, sensitive and economical method for the adsorptive voltammetric determination of trace amounts of Mo(VI) in organic matter rich environmental samples

A differential pulse adsorptive stripping voltammetric method has been developed for molybdenum trace determination in environmental water samples containing organic compounds. It was proved that interferences from the organic matrix such as surface active substances and humic substances could be removed by the addition of resin to the analysed sample prior to voltammetric measurement. The parameters for Mo(VI) determination in the presence of resin, using a hanging mercury drop as the working electrode, were examined systematically for two complexing agents: cupferron and chloranilic acid. The detection limits estimated from 3 times the standard deviation for a low Mo(VI) concentrations were equal to 5 × 10⁻¹¹ and 3 × 10⁻¹⁰ mol L⁻¹ for cupferron and chloranilic acid, respectively. At the optimized conditions the quantitative Mo(VI) determination in the presence of even 50 mg L⁻¹ of surface active compounds can be performed. The proposed procedures were validated in the course of Mo(VI) determination in certified reference material NASS-5 and in the course of studying recovery of Mo(VI) from spiked river water samples.     

Voltammetry as a tool for rough and rapid characterization of dissolved organic matter in the drainage water of hydroameliorated agricultural areas in Croatia

This study demonstrates the potential of the electrochemical methods for the characterization of dissolved organic matter (DOM) in the drainage water of hydroameliorated agricultural areas. A study of drainage water could lead to a better understanding of the distribution and fate of terrestrial DOM in the freshwater systems. We have applied the voltammetric techniques which were developed by our group for the characterization of organic matter in the natural waters in general. Studied samples were collected in the experimental amelioration fields in the Sava river valley (45^° 33′ 52″ N/16° 31′ 33″ E, 100 m above sea level), in the hydroameliorated agricultural areas in Croatia. The rough characterization of the type, nature and reactivity of DOM was done through the study of surface activity (SA) of dissolved organic carbon (DOC), copper complexing capacity (CuCC) and apperent stability constants, and measurements of organic and inorganic reduced sulfur species (RSS) fractions. The results confirm that the electrochemical approach gives a valuable and comprehensive insight into physicochemical characteristics of DOM in the drainage water and could be successfully applied to temporal studies in different terrestrial ecosystem.     

Novel approaches to the quantification of heavy metals on mercury-graphite electrodes in deep ocean waters

A procedure for the voltammetric determination of trace Zn(II), Pb(II), Cu(II), Cd(II), and Mn(II) in deep ocean water samples using a mercury-graphite electrode (MGE) is proposed. The generation of the MGE directly in the test solution ensures the autonomous performance of sequential stripping voltammetric analysis of samples in the field and substantially reduces the amount of the used distilled water.     

The role of low levels of water in the electrochemical oxidation of α-tocopherol (vitamin E) and other phenols in acetonitrile

The phenol, α-tocopherol, can be electrochemically oxidised in a -2e(-)/-H(+) process to form a diamagnetic cation that is long-lived in dry organic solvents such as acetonitrile and dichloromethane, but in the presence of water quickly reacts to form a hemiketal. Variable scan rate cyclic voltammetry experiments in acetonitrile with carefully controlled amounts of water between 0.010 M-0.6 M were performed in order to determine the rate of reaction of the diamagnetic cation with water. The water content of the solvent was accurately determined by Karl Fischer coulometric titrations and the voltammetric data were modelled using digital simulation techniques. The oxidation peak potential of α-tocopherol measured during cyclic voltammetry experiments was found to shift to less positive potentials as increasing amounts of water (0.01-0.6 M) were added to the acetonitrile, which was interpreted based on hydrogen-bonding interactions between the phenolic hydrogen atom and water. Several other phenols were examined and they displayed similar voltammetric features to α-tocopherol, suggesting that interactions of phenols with trace amounts of water were a common occurrence in acetonitrile. The H-bonding interactions of α-tocopherol with water were also examined via NMR and UV-vis spectroscopies, with the voltammetric and spectroscopic studies extended to include other coordinating solvents (dimethyl sulfoxide and pyridine).     

Stripping Voltammetric Determination of Uranium Traces in Sea Water Samples: Effect of Surfactants on the Measurements

The variables affecting determination of ultra trace levels of uranium (VI) in aqueous samples by differential pulse cathodic stripping voltammetry using chloranilic acid as the complexing agent have been examined in detail. Effect of organic surfactants on the voltammetric behavior has been studied. Electrochemical impedance measurements reveal the effect of adsorption of different surfactants on the adsorption pre-concentration step of uranium-chloranilic acid complex. Additionally, to better understand the analytical feature of the method, physicochemical aspects of the preconcentration process has been studied. Adsorption of uranium-chloranilic acid complex follows the Langmuir adsorption isotherm. Analysis results on sea water samples from India are reported.     

Enhancing the Efficiency of Anodic Stripping Voltammetry in Systems Permitting a Change of the Solution without Opening the Circuit

A new design for a transducer for voltammetric stripping analysis was proposed. It allows electroaccumulation and electrostripping stages to be carried out in the solutions of different compositions without opening a circuit. The potentialities of the transducer were demonstrated in the analysis of samples containing complex salt and organic matrices without their preliminary mineralization.     

Determination of Ethylenethiourea (ETU) at Trace Levels in Water Samples by Cathodic Stripping Voltammetry

A stripping voltammetric method for the determination of ethylenethiourea in water samples is described based on its adsorptive deposition at the hanging mercury drop electrode (HMDE). In a borate buffer (pH 9.0) as supporting electrolyte, ETU is deposited at +100 mV (vs. Ag/AgCl) and stripped during the cathodic scan. The linear range for the measurements was from 2.0 to 100 μg L^?1, with a detection limit calculated as 1.4 μg L^?1 after a deposition time of 300 s and a RSD of 1.9% (n=5) for 50 μg L^?1 of ETU measured. The interferences of some organic compounds and metallic ions were tested. Recoveries between 93 and 110% were obtained using the standard addition method for spiked samples of natural and drinking waters. The method is rapid and applicable in the monitoring of ETU residues in water samples.     

Electroanalytical method for determination of the pesticide dichlorvos using gold-disk microelectrodes

This paper reports the use of laboratory-prepared gold microelectrodes and square-wave voltammetry for analytical determination of low concentrations of the pesticide dichlorvos in pure and natural water samples. After optimization of the experimental and voltammetric conditions, the best voltammetric responses—current intensity and voltammetric profile—were obtained in 0.1 mol L^–1 NaClO₄ with f=100 s^–1, a=50 mV, and E_s=2 mV. The observed detection and quantification limits in pure water were 7.8 and 26.0 g L^–1, respectively. The reproducibility and repeatability of the method were also determined; the results were 1.4% (n=5) and 1.2% (n=10), respectively. Possible interfering effects were evaluated in natural water samples collected at different points with different levels of contamination from agricultural, domestic, or industrial waste from an urban stream. Results showed that the detection and quantification limits increased as a function of the quantity of organic matter present in the samples. Nonetheless, the values observed for these method characteristics were below the maximum value allowed by the Brazilian code for organophosphorus pesticides in water samples. Recovery curves constructed using the standard addition method were shown to be satisfactory compared with those obtained from high-performance liquid chromatography, confirming the suitability of the method for analysis of natural water samples. Finally, when the method was used to determine dichlorvos in spiked cows milk samples, satisfactory recovery and relative standard deviations were obtained.     

Simple and Simultaneous Determination of Free Chlorine, Free Bromine and Ozone in Water by LC

A simple liquid chromatographic method has been established for the simultaneous determination of free chlorine, free bromine, and ozone generated in electrical discharges. The method is based on the formation of organic derivatives, 4-halo-2,6-dimethylphenols with 2,6-dimethylphenol (2,6-DMP). The direct substitution reaction between halogens and 2,6-DMP was used for the determination of free chlorine, free bromine and ozone in water. For the determination of ozone, iodide was added 5 min after the addition of 2,6-DMP. The detection limits were about 2.0, 3.0 and 4.0 μg L^?1 for hypochlorite, hypobromite and ozone, respectively. The method was very simple and reproducible enough to permit the simultaneous analysis of each disinfectant in surface water or sea water in the presence of the mixture of disinfectants.