Use of polyurethane foam and 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline for determination of nitrite by diffuse reflectance spectroscopy and colorimetry

Polyurethane foam (PUF) has been suggested as a solid polymeric reagent for determination of nitrite. The determination is based on the diazotization of end toluidine groups of PUF with nitrite in acidic medium followed by coupling of polymeric diazonium cation with 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline. The intensely colored polymeric azodye formed in this reaction can be used as a convenient analytic form for the determination of nitrite by diffuse reflectance spectroscopy (c _min = 0.7 ng mL⁻¹). The possibility of using a desktop scanner, digital camera, and computer data processing for the numerical evaluation of the color intensity of the polymeric azodye has been investigated. A scanner and digital camera can be used for determination of nitrite with the same sensitivity and reproducibility as with diffuse reflectance spectroscopy. The approach developed was applied for determination of nitrite in river water and human exhaled breath condensate.     

Effect of surfactants on the determination of nitrite and nitrate in water samples

Summary The effect of four surfactants on the determination of nitrite and nitrate has been examined. The method which has been tested for nitrite is based on the formation of an azodye. The results show that cationic and non-ionic surfactants do not interfere with the determination of nitrite while anionic surfactants cause significant interferences, which could be eliminated by treating the water samples with a cationic surfactant.Two methods have been tested for the determination of nitrate in the presence of surfactants. One method is based on the nitration of salicyclic acid, while the other is based on the reduction of nitrate to nitrite. Results for the first method show that the non-ionic surfactant Triton-X causes significant interferences. Cationic and anionic surfactants do not interfere, when their concentration is relatively low. For higher concentrations an increasing interference is observed. Results for the second method show effects similar to those obtained for nitrite.

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Wirkung oberflächenaktiver Substanzen auf die Bestimmung von Nitrit und Nitrat in Wasserproben

     

Lignosulfonate‐Modified Electrode for Electrocatalytic Reduction of Acidic Nitrite

Sodium lignosulfonate (LS) undergoes oxidative electropolymerization on a glassy carbon (GC) electrode from sulfuric acid solution to form a chemically modified electrode exhibiting anionic character and redox activity. Cyclic voltammetry reveals the existence of two redox systems at E°′ values of +0.29 and +0.53 V, respectively. Peak currents are proportional to the scan rate as expected for surface confined systems. The GC|poly‐LS electrode shows electrocatalytic activity toward the reduction of acidic nitrite. When operating in a constant potential amperometric mode (at 0.0 V, vs. Ag/AgCl), a linear relationship between nitrite concentration and reduction current is observed over the range of 1 to 250 μM. The detection limit reaches 0.3 μM (S/N=3). The electrode may be practically applied for nitrite determination in human saliva.     

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.     

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.     

Supramolecular structural and spectral perspectives of novel ruthenium(III) azodye complexes

Five bis-[5-(4′-R-phenylazo)-8-hydroxyquinoline] ruthenium complexes [RuLn?·?Cl₂?·?OH₂]; where Ln?=?5-(4′-R-phenylazo)-8-hydroxyquinolinol, R?=?OCH₃ (n?=?1), CH₃(2), H(3), Cl(4), NO₂(5), have been prepared and characterized on the basis of elemental analyses, IR, ¹H NMR, ESR, thermal analysis and magnetic susceptibility measurements. The data show that these complexes exist in trans-isomeric solid form. Two inversion-related ligands and two Ru³⁺ atoms form a cage-like dimer. Both ligands of the dimer are bridged by a pair of inversion-related Ru–N (azodye) bonds. The octahedral coordination geometry of Ru³⁺ is made up of an N of pyridine, the deprotonated quinoline O atom, one of the azodye N atoms, two chlorides and one water. The ligands in the dimer are stacked over one another. In the solid state of azo-8-hydroxyquinoline, the dimers have inter-and intramolecular hydrogen bonds. Interactions between the ligands and the metal are discussed. The azo group was involved in chelation for all the prepared complexes. The effect of Hammet's constant on the ligand field parameters are also discussed and drawn.     

Dosierung kleiner Stickstoffdioxid-Mengen und Bestimmung des „Saltzman-Faktors“

A dynamic flow system is described by which N₂O₄ is diluted with air in 2 steps, to yield NO₂ concentrations in the partsper-million range. Part of the system is thermostatized. The final NO₂ concentration of the mixture can be calculated by taking into account the temperature and partial pressure dependent dissociation of N₂O₄. This system is used to test the Saltzman method, a photometric assay for the determination of NO₂, based on the formation of an intensely coloured azodye. The results obtained with gaseous NO₂ on one hand and with the equivalent amounts of aqueous nitrite solution on the other are compared. At a concentration of 1.5 μg NO₂ per 25 ml absorbing solution, the dye formation by 1 Mole of NO₂ equals that of 1 Mole of nitrite (“Saltzman-factor” 1.0). If the concentration is 10 μg/25 ml, the intensity of the colour effect due to 1 Mole of NO₂ equals 0.86 Moles of nitrite (“Saltzman-factor” 0.86). Only half the expected colour intensity was found when a NO₂-air-mixture was used that had been prepared by a dynamic two-step dilution and oxidation of NO (“Saltzman-factor” 0.5).     

Sequential Spectrophotometric Determination of Microgram Amounts of Nitrate and Nitrite in Mixtures

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.     

Electrocatalytical Oxidation of Nitrite and Its Determination Based on Au@Fe3O4 Nanoparticles

A promising electrochemical nitrite sensor was fabricated by immobilizing Au@Fe₃O₄ nanoparticles on the surface of L ‐cysteine modified glassy carbon electrode, which was characterized by scanning electron microscopy, X‐ray photoelectron spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The proposed sensor exhibited excellent electrocatalytic activity toward nitrite oxidation. The kinetic parameters of the electrode reaction process were calculated, (1–α)n_α was 0.38 and the heterogeneous electron transfer coefficient (k) was 0.13 cm s^?1. The detection conditions such as supporting electrolyte and pH value were optimized. Under the optimized conditions, the linear range for the determination of nitrite was 3.6×10^?6 to 1.0×10^?2 M with a detection limit of 8.2×10^?7 M (S/N=3). Moreover, the as‐prepared electrode displayed good stability, repeatability and selectivity for promising practical applications.     

Colorimetric Determination Of Hydrogen Peroxide Based on Localized Surface Plasmon Resonance of Silver Nanoprisms Using a Microchannel Chip

Silver nanoprisms (AgNPrs) have unique optical phenomena due to their localized surface plasmon resonance that results in the extinction of light from the visible to the near-infrared spectral region. In this study, we propose the colorimetric determination of silver nanoprisms in microchannels using a smartphone camera. Image acquisition was performed by capturing an image of the colloidal solution of the silver nanoprisms in the microchannel using the transmitted light. Red, green, and blue chromaticity levels were extracted from the recorded images for further quantification of the silver nanoprisms. This technique was employed for the detection and colorimetric determination of hydrogen peroxide (H₂O₂). Good linearity between the change in the green chromaticity level and concentration of hydrogen peroxide was observed for values from 10 to 300?μM with an R² value of 0.9670. We anticipate that the developed methodology for the quantification of silver nanoprisms and hydrogen peroxide by monitoring the change in color in the images of transmitted light will enhance the development of simple, rapid, and reliable detection systems for quality control in the production of silver nanoprisms as well as in chemical sensor applications.     

A Nitrite Electrochemical Sensor Based on Boron‐Doped Diamond Planar Electrochemical Microcells Modified with a Monolacunary Silicotungstate Polyoxoanion

A new boron doped diamond microcells (BDD) was modified, for rapid, selective and highly sensitive determination of nitrite, using a coating film of polyoxometalates (POMs), formed by cyclic voltammetry on the molecular p‐phenylenediamine (PPD) functionalized BDD. The scanning electron microscopy (SEM) technique was used to examine the morphology of (PPD/SiW₁₁) modified (BDD) electrode. It was found that (SiW₁₁) layer was uniformly formed on the electrode surface. It was observed that (BDD/PPD/SiW₁₁) showed excellent electrocatalytic activities towards nitrite ion. Under the selected conditions, the anodic peak maximum at ?0.6 V was linear versus nitrite concentration in the 40 µM–4 mM range, and the detection limit obtained was 20 µM. The newly developed electrode has been successfully applied to the determination of nitrite content in real river water samples.     

Determination of antioxidant activities in fruit juices based on rapid colorimetric measurement and characterisation of gold nanoparticles

A simple and green synthesis of gold nanoparticles (AuNPs) was achieved in tea solution and fruit juices with auric tetrachloride (HAuCl₄) without the addition of any other chemicals. Natural antioxidants present in tea leaves and fruit juices were able to reduce Au³⁺ ions to form AuNPs spheres with an average diameter of 22.9 ± 2.7 nm in the tea solution and 12.8 ± 2.4 nm in the orange juice. A colorimetric determination of antioxidant activities based on the formation of citrate-capped AuNPs has been developed. It was found that the colorimetric response of AuNPs was dependent on the concentration of antioxidants tested. As compared with the standard reference assay, i.e., the Folin–Ciocalteu method, the colorimetric method reported in this study showed a very good correlation (R² = 0.9996). The results indicate that the AuNPs-based colorimetric method provides a simple, effective and reliable measurement of the antioxidant capacity in the tested fruit juices.     

Electrooxidation of Nitrite Mediated by Cu‐x‐Tetraaminophenylporphyrin (x=2, 3, and 4) Glassy Carbon‐Modified Electrodes: Effect of Substituent Position

A study of glassy carbon electrodes modified with poly‐Cu‐x‐tetraaminophenylporphyrin (TAPP) (x=2, 3, and 4) toward the electrooxidation of nitrite is reported. The position of the amino group influences the degree of electropolymerization and the response toward the electrooxidation of nitrite. The influence of pH on the electrocatalytic oxidation of nitrite was also studied, finding that the activity is strongly pH‐dependent. For each system (polymeric porphyrins, poly‐Cu‐2‐TAPP, poly‐Cu‐3‐TAPP, and poly‐Cu‐4‐TAPP), the behavior of the modified electrode as amperometric nitrite sensor was studied at the best pH response, finding a linear correlation over a wide range of concentrations for poly‐Cu‐3‐TAPP. With poly‐Cu‐2‐TAPP, the range is smaller, and there is no linear relationship for poly‐Cu‐4‐TAPP. The plot of I_p vs. the square root of the scan rate shows a linear relationship for all the polymer systems, indicating that the electrooxidation of nitrite in the modified electrodes is a process controlled by diffusion. The Tafel slope was calculated, indicating that the determining step in the electrooxidation of nitrite varies depending on the position of the substituent, showing a dramatic change in the nature of the active sites.     

Improvement of sensitivity in flow analysis by exploiting a multi-reversed software-assisted system

A multi-reversed flow system software-assisted was developed for improvement of sensitivity in flow analysis. The performance of the flow system proposed was evaluated by using as a model the conventional Griess’ colorimetric reaction for determination of nitrite in waters. The manifold incorporated three 3-way solenoid valves, a relay box solenoid actuated, a peristaltic pump, and a photometric detector. A tailored software was designed and written in Visual Basic 6.0 which allows full control of all flow system components and simultaneous acquisition and processing of the data. The sensitivity measured as the slope of the calibration curve was improved 2.5- and 1.4-fold regarding those obtained by continuous- and stopped-flow systems, respectively. Other valuable features such as analytical throughput of 55 determinations per hour, limit of detection of 5 μg L⁻¹ (3σ_blank/slope), relative standard deviation < 2% (n = 8), and a linear dynamic range up to 1800 μg L⁻¹ were also achieved.     

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.     

N′-(3-Bromo-2-hydroxybenzylidene)isonicotinohydrazide and its oxovanadium(V) complex: synthesis,structures, and catalytic properties

A new hydrazone N′-(3-bromo-2-hydroxybenzylidene)isonicotinohydrazide (H₂L) and its oxovanadium(V) complex, [VOLL′]·2H₂O (L′ = 2-hydroxybenzohydroxamate), were prepared and structurally characterized by physico-chemical, spectroscopic methods, and single-crystal X-ray determination. The hydrazone coordinates to V through the phenolate oxygen, imino nitrogen, and enolate oxygen. The hydroxamate coordinates to V through the carbonyl oxygen and deprotonated hydroxyl oxygen. Vanadium in the complex is octahedral. The oxidation of olefins with the complex as catalyst was evaluated, which indicated that the complex showed catalytic efficiency in oxidation of several aliphatic and aromatic substrates under mild conditions, using tert-butyl hydrogen peroxide as oxidant.     

Disposable Screen‐Printed Edge Band Ultramicroelectrodes for the Determination of Trace Amounts of Nitrite Ion

The application of linear scan voltammetry for sensitive determination of nitrite by using a disposable screen‐printed edge band carbon ultramicroelectrode (designated as SPUME) was reported in this study. The measurement with the SPUME can be performed in solutions of low ionic strength, e.g., natural waters, because the ohmic loses are negligible. The limiting oxidation current of nitrite showed a wide linear range up to 3 mM at the SPUME. A relative standard deviation of 2.46% (n=5) for analyzing 5 μM nitrite indicated a detection limit (S/N=3) of 0.38 μM. Real sample analysis of mineral and ground water samples as well as bratwurst food product showed satisfactory results. Since the SPUME is low cost and easy for mass production, the disposable nature further offers to application in diverse field of electroanalytical chemistry.     

Development and Optimization of Twenty-Four Hour Manual Methods for the Collection and Colorimetric Analysis of Atmospheric NO2

Abstract

Manual twenty-four hour colorimetric procedures for the determination of atmospheric NO₂ are described. The methods are based on collecting NO₂ by bubbling ambient air for twenty-four hours through reagents that form stable nitrite solutions. The reagents described have a 93 % collection efficiency over the range of 20 to 750 μg/m³ NO₂ with no apparent interferences. The inadequacies' of the former reference or alkaline method¹ are also described.     

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.     

Small-volume fiber-optic evanescent-wave absorption sensor for nitrite determination

A novel small-volume fiber-optic evanescent-wave absorption sensor based on the Griess–Ilosvay reaction has been developed and evaluated for nitrite determination. The sensor was constructed by inserting a decladded optical fiber into a transparent capillary to form an annular column microchannel. The Evanescent wave (EW) field produced on the optical fiber core surface penetrated into the surrounding medium and interacted with the azo dye, which was generated by the reaction of nitrite and nitrite-sensitive reagents. The detector was designed to be parallel to the axis of the optical fiber. The defined absorbance was linear with the concentration of nitrite in the range from 0.05 to 10 mg L⁻¹, and the detection limit was 0.02 mg L⁻¹ (3σ) with the relative standard deviation (RSD) of 2.6% (n = 8). The present sensor was successfully used to determine nitrite in real samples of mineral water, tap water, rain water, and seawater. The results were consistent with the data obtained by standard spectrophotometric method, showing potential of the proposed sensor for practical application.