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1.
ABSTRACT An electrochemical method using linear sweep voltammetry techniques was developed to determine nitrite ion in aqueous solution in the presence of nitrate. Nitrite solutions exhibited a well-defined oxidation wave at +1.0V vs SCE at vitreous carbon, while no oxidation process was observed for nitrate solutions. The pH of the nitrite solutions varied from 2.37 to 5.60 and no change was observed in the Ep values, except for the pH 5.60 solution, where little change was verified. The potential also did not vary with change in the nitrite concentration in the 5.0 x 10 ?5 to 7.0 x 10 ?4 mol L ?1 range. Very good straight lines for plots of current versus nitrite concentration in the 7.0 x 10 ?5 to 7.0 x 10 ?4 mol L ?1 range were obtained; the correlation coefficient was never worse than 0.990. The nitrite determination was also performed in the presence of 1.0 x 10 ?3 mol L ?1 of NO 3 ? ions. The addition of NO 3 ? did not change significantly the current values even when it was added in one hundred times molar excess. 相似文献
2.
Abstract A simple spectrophotometric method for the trace determination of nitrite (NO ? 2) is described. Nitrite is reacted with Salbutamal sulphate in acidic medium which gives a yellow colour in alkaline medium (?pH 7) and can be determined in the presence of several cations and anions. Beer's law is obeyed in the range of 1.8 to 27.6 ppm of nitrite with the molar absorptivity 1.8 × 10 3 1 × mole ?1 × cm ?1 at 4l0 nm. The proposed method can also be utilized for the determination of nitrate (NO ? 3) after its reduction to nitrite. The method has been applied for the determination of various samples containing traces of nitrite. 相似文献
3.
This paper describes three new methods: the first may be used for the determination of nitrite; the second is applicable to determination of nitrate; and the third permits sequential determination of both nitrite and nitrate in mixtures with no prior separation. For the determination of nitrite and nitrate in synthetic mixtures containing 1:5 to 5:1 ratios of the ions, in tap water, and in river water, mean recoveries (for 3 to 22 μg of added NO −3and NO −2) are 96.1 and 98.1% ( n= 15) and coefficients of variation are 2.2 and 2.5% for NO −3and NO −2( n= 5), respectively. 相似文献
4.
The kinetics and nitroarene product yields of the gas-phase reactions of naphthalene- d8, fluoranthene- d10, and pyrene with OH radicals in the presence of NO x and in N 2O 5? NO 3? NO 2? air mixtures have been investigated at 296 ± 2 K and atmospheric pressure of air. Using a relative rate method, naphthalene- d8 was shown to react in N 2O 5? NO 3? NO 2? air mixtures a factor of 1.22 ± 0.10 times faster than did naphthalene, with the 1- and 2-nitronaphthalene- d7 product yields being similar to those of 1- and 2-nitronaphthalene from naphthalene. From the measured PAH concentrations and the nitroarene product yields, formation yields of 2-, 7-, and 8-nitrofluoranthene- d9 and 2- and 4-nitropyrene of 0.03, 0.01, 0.003, 0.005, and 0.0006, respectively, were determined from the OH radical-initiated reactions. Effective rate constants for the reactions of fluoranthene- d10 and pyrene with N 2O 5 in N 2O 5? ;NO 3? NO 2? air mixtures of ca. 1.8 × 10 ?17 cm 3 molecule ?1 s ?1 and ca. 5.6 × 10 ?17 cm 3 molecule ?1 s ?1, respectively, were derived. Formation yields of 2-nitrofluoranthene- d9 and 4-nitropyrene of ca. 0.24 and ca. 0.0006, respectively, were estimated for these reaction systems. 2-Nitropyrene was also observed to be formed in these N 2O 5? NO 3? NO 2 reactions, but was found to be a function of the NO 2 concentration and, therefore, would be a negligible product under ambient NO 2 concentrations. These product and kinetic data are consistent with ambient air measurements of the nitroarene concentrations. 相似文献
5.
Neural network software is described for processing the signals of arrays of ion-selective electrodes. The performance of the software was tested in the simultaneous determination of calcium and copper(II) ions in binary mixtures of copper(II) nitrate and calcium chloride and the simultaneous determination of potassium, calcium, nitrate and chloride in mixtures of potassium and calcium chlorides and ammonium nitrate. The measurements for the Ca 2+/Cu 2+ determinations were done with a pH-glass electrode and calcium and copper ion-selective electrodes; results were accurate to ±8%. For the K +/Ca 2+NO ?3/Cl ? determinations, the measurements were made with the relevant ion-selective electrodes and a glass electrode; the mean relative error was ±6%, and for the worst cases the error did not exceed 20%. 相似文献
6.
This study investigated the reactive dissolution of nitric oxide (NO) and nitrogen dioxide (NO2) mixtures in deionized water. The dissolution study was carried out in a flat surface type gas–liquid reaction chamber utilizing a gas flow-pattern resembling plasma jets which are often used in biomedical applications. The concentration of NO and NO2 in the gas mixtures was varied in a broad range by oxidizing up to 800 ppm of nitric oxide in Ar carrier gas with variable amount of ozone. The production of nitrite (NO2?) and nitrate (NO3?) in the water was proportional to treatment time up to 50 min. The concentration of NO3? was a power function of gas phase NO2 while the concentration of NO2? increased approximately linearly with gas phase NO2. The formation of NO2? and NO3? could be described by reactions between dissolved NO2 and NO in the water while the production rate was determined by diffusion-limited mass transport of nitrogen oxides to the bulk of the liquid. At higher NO2 concentrations, the formation of dinitrogen tetraoxide (N2O4) increased the formation rate of NO2? and NO3?. The identified mass transport limitation by diffusion suggests that convection of water created by the gas jet is insufficient and dissolution of nitrogen oxides can be increased by additional mixing. In respect of practical applications, the ratio of NO2? /NO3? in water could be varied from 0.8 to 5.3 with treatment time and gas phase NO2 and NO concentrations. 相似文献
7.
Abstract o-Phenylenediamine has been used as a reagent to quantify nitrites/nitrates in a variety of sample matrices. The method is based on the cyclization reaction between o-phenylenediamine and nitrite in acid medium. The amine undergoes diazotization with nitrite in the presence of acid to form the diazonium ion, which subsequently cyclizes to yield yellowish orange benzotriazole at room temperature with an absorption maximum at 450 nm. The formed dye has been separated, purified, and characterized by IR, NMR, and spectroscopy techniques. The parameters of the reaction between amine and nitrite have been optimized. The effect of interfering ions on the determination of nitrites/nitrates has been described. The developed method has been applied for the determination of residual NO 2 gas present in the ambient air after fixing it as a nitrite ion using sodium arsenite as a trapping medium. The dye formed has been extracted into organic solvent to improve the detection limit during the measurement of low levels of ambient NO 2 in air. The method obeyed Beer's law in the concentration range 0–250 µg in aqueous medium and 0–50 µg in organic medium with molar absorptivity of 4.09 × 10 4 L mol ?1 cm ?1 and 4.3 × 10 4 L mol ?1 cm ?1 respectively. Nitrate is determined by reducing it to nitrite after passing through the copperized cadmium reductor column. The developed method has been applied to determine nitrite/nitrate levels in water, soil, and biological samples. 相似文献
8.
Abstract A spectrophotometric method was developed to determine nitrite using safranin as color reagent. The reaction between nitrite and safranin produces a safranin-HNO 2 species, which exhibits absorption peaks at 280, 349, 420(shoulder) and 610 nm. The peak at 610 nm was chosen as the analysis wavelength because nitrite ion and safranin do not present absorption bands in this region. The Lambert-Beer law was obeyed in the concentration range 7.0 × 10 ?6 - 5.0 × 10 ?5M. The effects of various ions on absorbance of the safranin-HNO 2 species were studied; the nitrite analysis can be performed without interference in the presence of the ions SCN ?, Br ?, CH 3COO ?, Cl ? (≤ 1.0 × 10 ?3 M) and NO 3 ? (< 1.0 × 10 ?5 M). The SO 4 = does not interfere even at a concentration of 0.25M. 相似文献
9.
Peroxynitrite and nitrite ions are the diamagnetic products of photolysis (with light at a wavelength of 253.7 nm) of alkaline-earth nitrates; the paramagnetic products and hydrogen peroxide were not found. The structural water in alkaline-earth nitrate crystals did not affect the qualitative composition of the photodecomposition products. The quantum yield of nitrite ions was 0.0012, 0.0038, 0.0078, and 0.0091 quanta ?1 and that of peroxynitrite ions was 0.0070, 0.0107, 0.0286, and 0.0407 quanta ?1 for Sr(NO 3) 2, Ba(NO 3) 2, Ca(NO 3) 2 · 4H 2O, and Mg(NO 3) 2 · 6H 2O, respectively. 相似文献
10.
The yields of C 5 and C 6 alkyl nitrates from neopentane, 2-methylbutane, 2-methylpentane, 3-methylpentane, and cyclohexane have been measured in irradiated CH 3ONONO-alkane-air mixtures at 298 ± 2 K and 735-torr total pressure. Additionally, OH radical rate constants for neopentyl nitrate, 3-nitro-2-methylbutane, 2-nitro-2-methylpentane, 2-nitro-3-methylpentane, and cyclohexyl nitrate, relative to that for n-butane, have been determined at 298 ± 2 K. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10 ?12 cm 3 molecule ?1 s ?1, these OH radical rate constants are (in units of 10 ?12 cm 3 molecule ?1 s ?1): neopentyl nitrate, 0.87 ± 0.21; cyclohexyl nitrate, 3.35 ± 0.36; 3-nitro-2-methylbutane, 1.75 ± 0.06; 2-nitro-2-methylpentane, 1.75 ± 0.22; and 2-nitro-3-methylpentane, 3.07 ± 0.08. After accounting for consumption of the alkyl nitrates by OH radical reaction and for the yields of the individual alkyl peroxy radicals formed in the reaction of OH radicals with the alkanes studied, the alkyl nitrate yields (which reflect the fraction of the individual RO 2 radicals reacting with NO to form RONO 2) determined were: neopentyl nitrate, 0.0513 ± 0.0053; cyclohexyl nitrate, 0.160 ± 0.015; 3-nitro-2-methylbutane, 0.109 ± 0.003; 2-nitro-2methylbutane, 0.0533 ± 0.0022; 2-nitro-2-methylpentane, 0.0350 ± 0.0096; 3- + 4-nitro-2-methylpentane, 0.165 ± 0.016; and 2-nitro-3-methylpentane, 0.140 ± 0.014. These results are discussed and compared with previous literature values for the alkyl nitrates formed from primary and secondary alkyl peroxy radicals generated from a series of n-alkanes. 相似文献
11.
Rate coefficients for the gas‐phase reaction of isoprene with nitrate radicals and with nitrogen dioxide were determined. A Teflon collapsible chamber with solid phase micro extraction (SPME) for sampling and gas chromatography with flame ionization detection (GC/FID) and a glass reactor with long‐path FTIR spectroscopy were used to study the NO 3 radical reaction using the relative rate technique with trans‐2‐butene and 2‐buten‐1‐ol (crotyl alcohol) as reference compounds. The rate coefficients obtained are k(isoprene + NO 3) = (5.3 ± 0.2) × 10 ?13 and k(isoprene + NO 3) = (7.3 ± 0.9) × 10 ?13 for the reference compounds trans‐2‐butene and 2‐buten‐1‐ol, respectively. The NO 2 reaction was studied using the glass reactor and FTIR spectroscopy under pseudo‐first‐order reaction conditions with both isoprene and NO 2 in excess over the other reactant. The obtained rate coefficient was k(isoprene + NO 2) = (1.15 ± 0.08) × 10 ?19. The apparent rate coefficient for the isoprene and NO 2 reaction in air when NO 2 decay was followed was (1.5 ± 0.2) × 10 ?19. The discrepancy is explained by the fast formation of peroxy nitrates. Nitro‐ and nitrito‐substituted isoprene and isoprene‐peroxynitrate were tentatively identified products from this reaction. All experiments were conducted at room temperature and at atmospheric pressure in nitrogen or synthetic air. All rate coefficients are in units of cm 3 molecule ?1 s ?1, and the errors are three standard deviations from a linear least square analyses of the experimental data. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 57–65, 2005 相似文献
12.
Water homolyses upon vacuum-uv excitation into HO * radicals, hydrogen atoms and with lower efficiency, hydrated electrons. These primary species induce a series of reactions partially depleting nitrate and nitrite from aqueous solutions. Depletion rates depend on the presence of dissolved oxygen and temperature. Nitrate, nitrite, peroxynitrite and N 2O were identified as reaction products after irradiation of, either, nitrite and nitrate in aqueous solutions. A reaction mechanism is proposed in accord with the experimental facts and with the evidence given in the literature, where NO 2 * and NO * are key intermediates. NO 3 ?, NO 2 ?, NO 2 *, NO * O 2NO 2 ?, ONO 2 ? and N 2O, seem to be interrelated by many redox reactions and reaction equilibria where pH and the availability of electrons determine their occurrence. The proposed mechanism is supported by a computer program with which the observed experimental behavior could be simulated. 相似文献
13.
The kinetics and mechansim for the NO 2-initiated oxidation of tetramethyl ethylene (TME) have been studied using the FTIR spectroscopic method in mixtures containing NO 2 and TME (0.1?1.0 Torr) and N 2? O 2 (700 Torr) at 298 ± 2 K. While TME decayed according to - d[TME]/ dt = kobs[NO 2][TME], NO 2 exhibited a complex kinetic behavior. Furthermore, values of kobs were dependent on [O 2]. Among the products were (CH 3) 2CO and at least three NO 2-containing compounds. These results indicate the formation of a nitro-alkylperoxy radical via reactions (1), (?1), and (2), and its subsequent reactions leading to the observed products. The [O 2]-dependence of kobs yielded k1 = (1.07 ± 0.15) × 10 ?20 cm 3 molecule ?1 S ?1 and k?1/ k2 = (3.54 ± 0.61) × 10 18 molecule cm ?3. 相似文献
14.
The bimolecular rate coefficients k and k were measured using the relative rate technique at (297 ± 3) K and 1 atmosphere total pressure. Values of (2.7 ± 0.7) and (4.0 ± 1.0) × 10 ?15 cm 3 molecule ?1 s ?1 were observed for k and k, respectively. In addition, the products of 2‐butoxyethanol + NO 3? and benzyl alcohol + NO 3? gas‐phase reactions were investigated. Derivatizing agents O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine and N, O‐bis (trimethylsilyl)trifluoroacetamide and gas chromatography mass spectrometry (GC/MS) were used to identify the reaction products. For 2‐butoxyethanol + NO 3? reaction: hydroxyacetaldehyde, 3‐hydroxypropanal, 4‐hydroxybutanal, butoxyacetaldehyde, and 4‐(2‐oxoethoxy)butan‐2‐yl nitrate were the derivatized products observed. For the benzyl alcohol + NO 3? reaction: benzaldehyde ((C 6H 5)C(?O)H) was the only derivatized product observed. Negative chemical ionization was used to identify the following nitrate products: [(2‐butoxyethoxy)(oxido)amino]oxidanide and benzyl nitrate, for 2‐butoxyethanol + NO 3? and benzyl alcohol + NO 3?, respectively. The elucidation of these products was facilitated by mass spectrometry of the derivatized reaction products coupled with a plausible 2‐butoxyethanol or benzyl alcohol + NO 3? reaction mechanisms based on previously published volatile organic compound + NO 3? gas‐phase mechanisms. © 2012 Wiley Periodicals, Inc. 1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 778–788, 2012 相似文献
15.
High-pressure mass spectrometric measurements were carried out to examine the mechanism of NO 3? formation in pure gaseous ethyl nitrate and its binary mixtures with various bath gases. A novel reaction: NO 2? + C 2H 5ONO 2 → NO 3? + C 2 H 5 ONO occurring with an activation energy has been reported and evidence for collisional deactivation of the intermediate complex [NO 2 ·C 2H 5ONO 2 has been obtained. The calculations performed with semi-empirical MINDO/3 suggest that this reaction proceeds by the nucleopholic displacement mechanism. Attack of NO 2? on H-atom of the methyl group prefers the formation of clustered ion NO 2?sd C 2H 5ONO 2, which is experimentally observed. 相似文献
16.
Ion interaction reversed-phase liquid chromatography with octylammonium orthophosphate as the interacting reagent and a reversed-phase C 18 column was applied to the identification and determination of nitrite and nitrate in Venice lagoon water. Interference by the high chloride concentration was systematically studied and the results obtained with different column packings were compared. With spectrophotometric detection at 230 nm, nitrite at 0.005 mg 1 ?1 can be detected and determined even in the presence of 0.70 M chloride. The dependence of the retention time of nitrite on the chloride concentration was studied for two reversed-phase columns with different packings. Concentrations of 0.30 ± 0.05 mg 1 ?1 of nitrite and 0.20 ± 0.05 mg 1 ?1 of nitrate were found in Venice lagoon water. 相似文献
17.
The gas‐phase reactions of the NO 3 radical with 2‐methylthiophene, 3‐methylthiophene, and 2,5‐dimethylthiophene have been studied, using relative and absolute methods at 298 K. Determination of relative rate was performed using Teflon collapsible bag as the reaction chamber and gas chromatography as the analytical tool. For the absolute method, experiments were carried out using fast‐flow‐discharge technique with detection of NO 3 by laser‐induced fluorescence. The temperature dependence was studied by the absolute technique for the reactions of NO 3 with 2‐methylthiophene and 3‐methylthiophene in the range 263–335 K. The proposed Arrhenius expressions for the reaction of the nitrate radical with 2‐methylthiophene and 3‐methylthiophene are k = (4 ± 2) × 10 ?16 exp[?(2200 ± 100)/ T]] cm 3 molecule ?1 s ?1 and k = (3 ± 2) × 10 ?15 exp[?(1700 ± 200)/ T]] cm 3 molecule ?1 s ?1, respectively. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 286–293, 2003 相似文献
18.
Abstract A highly sensitive spectrophotometric method has been developed for the determination of nitrogen dioxide (nitrite as NO z ?) by reacting manganese dioxide in 1:20 perchloric acid. An amount of manganese dioxide (MnO z) equivalent to the concentration of nitrogen dioxide becomes soluble due to the reduction of Mn (IV) to Mn (II) by nitrite in acidic medium. The soluble Mn (II) ion is filtered to remove excess of MnO 2 and is oxidized to permanganate ion by periodic acid in presence of phosphoric acid. The violet colored solution shows maximum absorbance at 525 nm. The sensitivity of the method is 0.08 ppm based on 0.0044 absorbance, and Beer's law is obeyed in the concentration range of 0.2 to 10.0 μg/mL of NO 2 ?. Molar absorbance is found to be 2442 at 525 nm. In the present investigation NO 2 ? was treated with excess of MnO 2 in 1:20 perchloric acid where NO 2 ? reduces equivalent amount of Mn (IV) to Mn (II) and becomes soluble. The soluble Mn (II) was heated to boiling and 25 mg (approx.) periodic acid is added and cooled. The volume of each solution is made to 50 mL in volumetric flask. Reagent blank is prepared in similar way except sodium nitrite solution. The absorbance is measured at 525 nm against reagent blank. 相似文献
19.
The formation of nitrous acid (HONO) in the dark from initial concentrations of NO 2 of 0.1–20 ppm in air, and the concurrent disappearance of NO 2, were monitored quantitatively by UV differential optical absorption spectroscopy in two different environmental chambers of ca.4300- and 5800-L volume (both with surface/volume ratios of 3.4 m ?1). In these environmental chambers the initial HONO formation rate was first order in the NO 2 concentration and increased with the water vapor concentration. However, the HONO formation rate was independent of the NO concentration and relatively insensitive to temperature. The initial pseudo-first-order consumption rate of NO 2 was (2.8 ± 1.2) × 10 ?4 min ?1 in the 5800-L Teflon-coated evacuable chamber and (1.6 ± 0.5) × 10 ?4 min ?1 in a 4300-L all-Teflon reaction chamber at ca.300 K and ca.50% RH. The initial HONO yields were ca.40–50% of the NO 2 reacted in the evacuable chamber and ca.10–30% in the all-Teflon chamber. Nitric oxide formation was observed during the later stages of the reaction in the evacuable chamber, but ca.50% of the nitrogen could not be accounted for, and gas phase HNO 3 was not detected. The implications of these data concerning radical sources in environmental chamber irradiations of NO x? organic-air mixtures, and of HONO formation in polluted atmospheres, are discussed. 相似文献
20.
The aromatic ring-retaining products formed from the gas–phase reactions of the OH radical with benzene and toluene, in the presence of NO x, have been identified and their formation yields determined. These products, and their formation yields, are as follows: from benzene – phenol, 0.236 ± 0.044; nitrobenzene, {(0.0336 ± 0.0078) + (3.07 ± 0.92) × 10 ?16[NO 2]}; from toluene – benzaldehyde, 0.0645 ± 0.0080; benzyl nitrate, 0.0084 ± 0.0017; o?cresol, 0.204 ± 0.027; m? + p?cresol, 0.048 ± 0.009; m-nitrotoluene, {(0.0135 ± 0.0029) + (1.90 ± 0.25) × 10 ?16[NO 2]}, where the NO 2 concentration is in molecule cm ?3 units. The formation yields of o- and p-nitrotoluene from toluene were ca. 0.07 and 0.35 that of m-nitrotoluene, respectively. The observations that the nitro-aromatic yields do not extrapolate to zero as the NO 2 concentration approaches zero are not consistent with current chemical mechanisms for these OH radical-initiated reactions, and suggest that under the experimental conditions employed in this study the hydroxycyclohexadienyl radicals formed from OH radical addition to the aromatic ring react with NO 2 rather than with O 2. However, these data concerning the nitroaromatic yields are consistent with our previous conclusions that many of the nitrated polycyclic aromatic hydrocarbons present in ambient air are formed, at least in part, in the atmosphere from OH radical reactions. 相似文献
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