Determination of Nitrite Through S-Nitrosocaptopril Formation and Fluorescent Derivatization of Remaining Captopril Using o-Phthalaldehyde and Glycine

We have developed an indirect fluorescence method for the determination of nitrite based on two reactions. The S-nitrosocaptopril produced by the first reaction between nitrite and excess captopril is not fluorescent. The fluorescent product produced by the residual captopril with glycine and o-phthalaldehyde is then measured and related to the nitrite concentration. We have optimized comprehensively the reaction condition parameters, including the thiol regent for the two reactions, reaction temperature and pH value for the first reaction, and the choice of amino acid, pH value, the ratio of reactants, buffer concentration, reaction temperature, and time for the second fluorescence reaction. Potential interferences by 8 cations and 10 anions on the fluorescence intensity were slight except for iodate and periodate which could likely be removed by addition of a reducing agent. For the analytical figures of merit, the limits of detection and quantitation of nitrite are 0.8 and 2.5?nM, respectively. The fluorescence intensity is found to linearly decrease with increasing nitrite from 0 to 140?nM. The method has shown to have good interday (<8%) and intraday precision (1–4%). The formation of nitrite from nitrate due to microbial degradation of spinach can be easily followed. Although the method requires a two-step reaction sequence that takes a significant analysis time, the safety and cost of the reagents (no carcinogenic amino naphthalene compounds) as well as excellent analytical figures of merit are significant advantages.     

Electrocatalytic Oxidation of Nitrite at Gold Nanoparticle-polypyrrole Nanowire Modified Glassy Carbon Electrode

A novel chemically modified electrode based on the dispersion of gold nanoparticles on polypyrrole nanowires has been developed to investigate the oxidation behavior of nitrite using cyclic voltammetry, differential pulse voltammetry and chronoamperometry techniques. The diffusion coefficient (D), electron transfer coefficient (α) and charge transfer rate constant (k) for the oxidation of nitrite were determined. The modified electrode exhibited high electrocatalytic activity toward the oxidation of nitrite. The catalytic peak current was found to be linear with nitrite concentrations in the range of 8.0×10^?7?2.5×10^?3 mol·L^?1 with a detection limit of 1.0×10^?7 mol·L^?1 (s/n=3). The proposed method was successfully applied to the detection of nitrite in water samples with obtained satisfactory results. Additionally, the sensor also showed excellent sensitivity, anti‐interference ability, reproducibility and stability properties.     

Extractive spectrophotometric determination of trace amounts of nitrogen dioxide,nitrite, and nitrate

A sensitive extractive spectrophotometric method for the determination of nitrogen dioxide in air and nitrite and nitrate in water, soil and blood serum is described. Nitrogen dioxide in air is fixed as nitrite in a suitable trapping solution. The method is based on the diazo coupling reaction betweenp-nitroaniline andN-(1-naphthyl)ethylenediamme dihydrochloride [NEDA]. The azo dye formed under aqueous conditions is extracted with isobutyl methyl ketone [IBMK]. The system obeys Beer's law over the range 0–3 g of nitrite at 545 nm and the colour is stable for 3h. The molar absorptivity of the colour system is 5.7 × 10⁴ L mol^–1 cm^–1. The relative standard deviation is 1.3% for ten determinations at 2 ug of nitrite. Nitrate is determined as nitrite after reduction on a cadmium column. Negative interferences from SO₂, H₂S, Cu²⁺ and Cr³⁺ and positive interference from Fe²⁺ and Fe³⁺ can be simply masked.     

The oxidation and reduction behavior of nitrite at carbon nanotube powder microelectrodes

Carbon nanotube electrodes were fabricated using powder microelectrode method, and the carbon nanotube powder microelectrodes (CNTPMEs) were characterized by the electro-oxidation and electro-reduction of nitrite. It was found that the kinetics of oxidation and reduction were greatly improved at CNTs compared with that at conventional graphite, indicating that CNTs could catalyze the electrochemical process of nitrite. The kinetic parameters of these process at CNTs were calculated, i.e. k was 0.593 cm s⁻¹, and (1-α)n_α was 0.501±0.018 for the nitrite oxidation. This CNTPME was also used as a nitrite carbon nanotube sensor, and the results showed that the detection limit was 8 μM.     

Ultra-trace level determination of nitrite in human saliva by spectrofluorimetry using 1,3,5,7-tetramethyl-8-(3,4-diaminophenyl)-difluoroboradiaza-s-indacene

A rapid, highly sensitive and selective fluorogenic method for the determination of traces of nitrite is described. It is based on the reaction of weakly fluorescent 1,3,5,7-tetramethyl-8-(3,4-diaminophenyl)-difluoroboradiaza-s-indacence (DAMBO) and nitrite in acidic aqueous solution to give 1,3,5,7-tetramethyl-8-(5-benzotriazolyl)-difluoroboradiaza-s-indacene (DAMBO-T), which is highly fluorescent. The optimum reaction conditions and other analytical parameters are investigated to enhance the sensitivity of the method. The fluorescence enhancement at 507 nm is linearly related to the concentration of nitrite in the range of 6.0 × 10⁻⁹–5.0 × 10⁻⁷ mol L⁻¹ with a correlation coefficient of R = 0.9995 (n = 10) and a detection limit of 1.0 × 10⁻¹⁰ mol L⁻¹. The R.S.D. is 1.12% (n = 10). The method is applied to the determination of nitrite in human saliva samples with the recoveries of 96. 24–105.30%. Correspondence: Ke-Jing Huang, Department of Chemistry, Wuhan University, Wuhan 430072, P.R. China     

Poly(ortho‐toluidine) Modified Carbon Paste Electrode: A Sensor for Electrocatalytic Reduction of Nitrite

The electrocatalytic reduction of nitrite has been studied by poly(ortho‐toluidine) films modified carbon paste electrode (P‐OT/MCPE). Cyclic voltammetry and chronoamperometry techniques were used to investigate the suitability of poly(ortho‐toluidine) as a mediator for the electrocatalytic nitrite reduction in aqueous solution with various pH. Results showed that pH 0.00 is the most suitable for this purpose. In the optimum pH, the reduction of nitrite occurs at a potential about 600 mV more positive than unmodified carbon paste electrode. The catalytic reaction rate constant, (k_h), was calculated 8.68×10² M^?1 s^?1 by the data of chronoamperometry. The catalytic reduction peak current was linearly dependent on the nitrite concentration and the linearity range obtained was 5.00×10^?4 M–1.90×10^?2 M. Detection limit has been found to be 3.38×10^?4 M (2σ). This method has been successfully employed for quantification of nitrite in real sample.     

Sensitive determination of nitrite by means of a Landolt-type reaction in fluorescent aggregates of a binaphthyl-based amphiphile

The iodine quenching effect on the fluorescence of a binaphthyl-based amphiphile, C₈BNC₆N, was used for monitoring the Landolt-type reaction between nitrite, iodide, and thiosulfate. Due to the possibility of iodine detection in the 10^–8–10^–7 M range, and to the effective concentration of anionic reagents on the surface of cationic aggregates, the indicator reaction can be monitored using reagents at concentration levels as low as 10^–7 M. To optimize the analytical system, the effect of pH and reagent concentrations on the rate of indicator reaction were studied. The influence of the matrix of water samples and effect of side-reactions increasing the value of a blank test were examined. A procedure for nitrite determination in water was developed, using the diazo reaction for selective nitrite removal to provide a reference solution, which avoided possible effects of the matrix components. The usefulness of this method was tested by determining trace amounts of nitrite in water samples. The procedure allows determination of nitrite down to 5 ng/ml (detection limit about 2ng/ml) with r.s.d. of 10% in the 20–250 ng/ml range.     

Bestimmung von Mikromengen Nitrit neben Nitrat mit 2,7-Diaminofluoren

Zusammenfassung Eine empfindliche und selektive spektrophotometrische Methode zur Bestimmung kleiner Mengen Nitrit mit 2,7-Diaminofluoren wurde beschrieben. Das Lambert-Beersche Gesetz wird zwischen 0,1 und 2,3g/ml streng befolgt. 47 Anionen und Kationen wurden auf ihre Störeffekte untersucht. Eine Arbeitsweise für natürliche Wässer wurde angegeben. Durch Reduktion des Nitrats mit Cadmium kann die Summe der Nitrate und Nitrite als Nitrit bestimmt werden.

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Determination of microquantities of nitrite in the presence of nitrate with 2,7-diaminofluorene

Summary A sensitive and selective method of spectrophotometric determination of small quantities of nitrite in the presence of nitrate with 2,7-diaminofluorene is described. Lambert-Beer's law is strictly obeyed between 0,1 and 2,3g/ml 47 anions and cations concerning their interference are studied. A method for natural waters is described. The sum of nitrate and nitrite can be determined as nitrite after all the nitrate is reduced to nitrite with cadmium.

     

Rapid determination of nitrite in foods in acidic conditions by high‐performance liquid chromatography with fluorescence detection

In this study, a simple, rapid, and sensitive method for the determination of nitrite (NO₂^?) in food samples by high‐performance liquid chromatography with fluorescence detection in acidic conditions had been developed. The derivatization of the nitrite with 2,3‐diaminonaphthalene was performed in acidic conditions to yield the highly fluorescent 2,3‐naphthotriazole, which was directly analyzed by high‐performance liquid chromatography with fluorescence detection without adjusting the solution to alkaline. The analysis column was reversed‐phase C₈ column. A constant flow rate of 1.0 mL/min was employed using water/acetonitrile as the mobile phase in isocratic mode (70:30, v/v). Fluorescence was monitored with excitation at 375 nm and emission at 415 nm. The standard calibration curves were linear for nitrite in different matrixes in the concentration range of 0–100 μg/L, and the correlation coefficients ranged from 0.9978 to 0.9998. The limits of detection and quantification were in the ranges of 0.012–0.060 and 0.040–0.20 mg/kg, respectively. The recoveries of nitrite from samples spiked at three different concentrations were 74.0–113.2%, and the relative standard deviations of the recovery results (n = 6) were 1.67–10.8%. The proposed method has good repeatability and is very sensitive and simple. It has been successfully used to determine nitrite in foods.     

Pencil Lead Electrode Modified with Hemoglobin Film as a Novel Biosensor for Nitrite Determination

In the present paper, the electrochemical reduction of nitrite at a hemoglobin modified pencil lead electrode (Hb/PLE) is described. The electrochemical properties of nitrite were studied by cyclic voltammetry and chronoamperometry. Results showed that the hemoglobin film has an excellent electrochemical activity towards the reduction of nitrite. By using voltammetric and chronoamperometric methods, α, n_α and n were calculated. Then the ability of the electrode for nitrite determination was investigated using differential pulse voltammetry. The electrocatalytic reduction peak currents were found to be linear with the nitrite concentration in the range from 10 to 220 µM with a detection limit of 5 µM. The relative standard deviation is 2 % for 3 successive determinations of a 100 µM nitrite solution. This modified electrode was successfully used for the detection of low amounts of NO₂^? in spinach sample and a spiked sample of tap water.     

Electrochemical sensor of nitrite based on an inorganic film modified glassy carbon electrode

The electrocatalysis of nitrite in solutions at an inorganic film modified glassy carbon electrode was studied. The modifier was an electrodeposited thin inorganic film of the copper-heptacyanonitrosylferrate (CuHNF). Cyclic voltammetry of the modified electrode in a nitrite solution revealed that both oxidation and reduction of nitrite were catalyzed and the electrocatalytic currents were controlled by the diffusion of nitrite. Voltammetric and amperometric responses were investigated. When applied as an amperometric sensor in a flow injection system, the modified electrode permitted detection at — 0.55 V, over 500 mV lower than at the naked electrode surface. A linear response range extending from 1 × 10^–6 to 1 × 10^–3 M nitrite was obtained, with a detection limit of 3 × 10^–7 M. The relative standard deviation for 50 repetitive injections with a 5 × 10^–5 M nitrite solution was less than 4%. The procedure was applied to the determination of nitrite in saliva and nitrate.     

Activated Copper Cathodes as Sensors for Nitrite Analysis

The increased surface area of copper electrodes upon applying a suitable potential protocol was characterized by atomic force microscopy images. Scanning electrochemical microscopy was used to demonstrate the enhanced reactivity of the generated surface. The modified electrode showed excellent catalytic activity towards nitrite reduction in acidic medium (pH 2). This new platform was used in the development of a fast and simple voltammetric method for nitrite determination. Commercial and rainwater spiked samples were analyzed and the data showed an excellent agreement with those obtained with a reference spectrophotometric method (Griess reaction) at a confidence level of 95 % (Student’s t‐test).     

Removal of nitrite with sulfamic acid for nitrate N and O isotope analysis with the denitrifier method

In environmental water samples that contain both nitrate (NO) and nitrite (NO), isotopic analysis of nitrate alone by all currently available methods requires pretreatment to remove nitrite. Sulfamic acid addition, used previously for this purpose (Wu JP, Calvert SE, Wong CS. Deep‐Sea Research Part I – Oceanographic Research Papers 1997; 44: 287), is shown here to be compatible with the denitrifier method for both N and O isotope analysis of nitrate. Sulfamic acid at a pH of ～1.7 reduces nitrite to N₂. Samples are then neutralized with base prior to isotope analysis, to alleviate the buffering demands of the bacterial media and as a precaution to prevent modification of nitrate during storage with the residual sulfamic acid at low pH. Under appropriate reaction conditions, nitrite is completely removed within minutes. Sulfamic acid treatment does not compromise the completeness of the conversion of nitrate into N₂O or the precision and accuracy of N and O isotope measurements by the denitrifier method. Nitrite concentrations upwards of 7 times the ambient nitrate can be removed without affecting the isotope composition of nitrate. The method is applied to analyses of the coupled N and O isotopes of nitrate and nitrite in waters of the Mexican Margin, to illustrate its efficacy and utility when employed either in the field upon sample collection or in the lab after months of frozen sample storage. Copyright © 2009 John Wiley & Sons, Ltd.     

Nitration‐Oximization of Styrene Derivatives with tert‐Butyl Nitrite: Synthesis of α‐Nitrooximes

A highly efficient method for direct nitration‐oximization of styrene derivatives using tert‐butyl nitrite (t‐BuONO) in DMSO was developed. The present method offers a convenient and practical approach for the synthesis of α‐nitrooximes in moderate to high yields. The salient features entail mild reaction conditions, metal‐free reagent, environmentally benign solvent and simple experimental procedure.     

Comparison of three post-column reaction methods for the analysis of bromate and nitrite in drinking water

Three post-column ion chromatographic methods (i.e., a sodium bromide–sodium nitrite method, an o-dianisidine method, and a potassium iodide–ammonium heptamolybdate method) were compared for bromate and nitrite analysis. Also, the effect of direct mixing of the reagents without ion suppressors for the sodium bromide–sodium nitrite method and the potassium iodide–ammonium heptamolybdate method was investigated. For the analysis of bromate, the three methods showed similar method detection limits (0.17–0.24 μg/l) with pneumatic reagent delivery systems. Direct reagent mixing achieved comparable detection limits to the suppressor configuration. The three methods are also compatible with conductivity detection. When used in combination with conductivity detection, this compatibility allows simultaneous analysis of bromate, nitrite, and other common ions in drinking water, such as bromide. It was found that the o-dianisidine method achieves μg/l-level detection of nitrite and bromate with a simpler configuration than the potassium iodide–ammonium heptamolybdate method, while the sodium bromide–sodium nitrite method was not sufficiently sensitive for nitrite analysis at the μg/l level.     

A hydrophobic deep eutectic solvent‐based vortex‐assisted dispersive liquid–liquid microextraction combined with HPLC for the determination of nitrite in water and biological samples

In recent years, hydrophobic deep eutectic solvents as new generation of green solvents have attracted wide attention in liquid microextraction technique. In this article, four hydrophobic deep eutectic solvents composed of trioctylmethylammonium chloride and oleic acid were designed and prepared firstly. Combined with high‐performance liquid chromatography, these deep eutectic solvents were used as an extraction solvent in vortex‐assisted dispersive liquid–liquid microextraction for the selective enrichment and indirect determination of trace nitrite from real water and biological samples. This method is based on the diazotization‐coupling reaction of nitrite with p‐nitroaniline and diphenylamine in acidic water, and then the nitrite is quantified indirectly by measuring the obtained azo compounds. Some factors influencing the extraction efficiency, including the reaction and extraction conditions, were investigated. Under the optimized conditions, the method has a linear range of 1–300 μg/L with a correlation coefficient of 0.9924, limit of detection of 0.2 μg/L, limit of quantitation of 1 μg/L, intraday and interday relative standard deviations of 4.0 and 6.0%. This method was successfully applied in determination of nitrite from three environmental water and two biological samples with the recovery in the range of 90.5–115.2%. In addition, these results were well agreement with those obtained by the conventional Griess method.     

Spectrophotometric Determination of Hydrazine

Abstract

A simple sensitive and selective method is described for the determination of trace amounts of hydrazine. The method is based on the reduction of nitrate to nitrite. Hydrazine in ammoniacal condition is used as reducing agent with copper(II) as catalyst. The nitrite prepared is determined based on the diazo coupling reaction between p‐nitroaniline and N‐(1‐naphthyl)ethylenediammine dihydrochloride(NEDA). The method obeys Beer's law in the concentration range of 0–15 µg of hydrazine in a sample volume of 10 ml at 545 nm and the colour is stable for 3 h. The molar absorptivity is calculated to be 3.83×10⁴ l/mol/cm with a correlation coefficient of 0.999. The relative standard deviation is 1.8% (n=10) at 12 µg of hydrazine. Interferences due to foreign ions have been studied and the method has been applied for the determination of hydrazine in boiler feed water.     

A Novel Flow-Injection System for Simultaneous Determination of Nitrate and Nitrite Based on the Use of a Zinc Reductor and a Bulk Acoustic Wave Impedance Detector

A novel flow-injection system has been developed for the simultaneous determination of nitrate and nitrite present in water, foodstuffs, and human saliva. The system is based on the use of a zinc-filled reduction column and a bulk acoustic wave impedance sensor (BAWIS) as detector. With water as carrier stream, both nitrate and nitrite are converted on-line to ammonia, whereas with sulfamic acid, only nitrate is converted to ammonia. The ammonia formed diffuses across a PTFE membrane and is trapped in an acid stream causing a change in the solution conductance, which is monitored by a BAWIS detector. At a throughput of about 60 h⁻¹, the proposed system exhibited a linear response to the concentration of nitrate and nitrite from 2.5 μM to 1.00 mM, with detection limits of 1.7 and 1.8 μM, respectively, and the relative standard deviation of the peak heights (n= 6) ranged between 0.83 and 1.75% for the entire working range. In analysis of real samples, the simultaneous determination of nitrate and nitrite was achieved by the proposed method with a simple change of the carrier stream between water and sulfamic acid, and the results agreed well with those of conventional colorimetry.     

Electrocatalytic Reduction of Nitrite by Phosphotungstic Heteropolyanion. Application for Its Simple and Selective Determination

Three couples of reversible redox peaks of the PW₁₂O₄₀^3? (PW₁₂) anion, which are composed of two one‐electron and one two‐electron processes occur in the potential range from +0.25 to ?0.7 V in aqueous solutions. The electrocatalytic reduction of nitrite has been studied by the first redox couple of the PW₁₂ anion at the surface of a carbon paste electrode. Cyclic voltammetric and chronoamperometric techniques were used to investigate the suitability of PW₁₂ anion as a mediator for nitrite electrocatalytic reduction in aqueous solution with strongly acidic concentration of H₂SO₄. Results showed that H₂SO₄ 1.00 M is the best medium for this purpose. In the optimum concentration of H₂SO₄, the electrocatalytic ability about 500 mV can be seen and the homogeneous second‐order rate constant (k_s) for nitrite coupled catalytically to PW₁₂ anion was calculated as 2.52×10³ M^?1 s^?1 using the Nicholson–Shain method. According to our voltammetric experiments, the catalytic reduction peak current was linearly dependent on the nitrite concentration and the linearity range obtained was 3×10^?5 to 1.00×10^?3 M. The detection limit has been found to be 2.82×10^?5 M (2σ). This method has been applied as a selective, simple, and precise method for determination of nitrite in real samples.     

Analytical possibilities of digital colorimetry: Determination of nitrite using polyurethane foam

Using the example of the determination of nitrite as polymeric azodye, the possibility of using office scanners, digital cameras, and computer data processing in different colorimetric coordinate systems (RGB, CMYK, LAB, and HSV) has been studied. Polymeric azodye was obtained by an azocoupling reaction between diazotized polyurethane foam (PUF) with 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline. The analytically important colorimetric coordinates in these systems were revealed and compared and the coordinates that result in the maximum sensitivity of nitrite determination were chosen. It was shown that calibration curves of the colorimetric coordinates versus concentration of nitrite in aqueous solution can be described by a first-order exponent. The detection limits of nitrite (1–3 ng/ml) were achieved in the RGB and CMYK colorimetric systems.