New spot tests for nitrates and nitrites

New spot test reactions for the nitrates and nitrites are described. These are based on a reaction with hydroquinone whereby nitric oxide and chloranil are produced. Nitric oxide is detected in the gas phase by the Griess reaction and chloranil is determined by a reaction with tetra base. Nitrate and nitrite ions are also detected in presence of each other. Some organic and inorganic nitrate samples are tested, the lower limit of identification being 50 μg.     

Determination of nitrite ions using test strips based on 3-hydroxy-7,8-benzo-1,2,3,4-terahydroquinoline

RIB-Nitrite-Test and Sorbfil-Nitrite-Test strips were developed for determining nitrite ions in water samples and foodstuffs by a reaction similar to the Griess reaction. Stable and noncarcinogenic 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline was used as an azo component adsorbed in the reagent paper zone on a polymeric support or on a Sorbfil plate sealed in a transparent polymeric film. Performance characteristics were evaluated by a statistical method for visual test procedures for the detection and determination of NO ₂ ^? using two different test strips. The determination limit was 0.54 and 0.09 mg/L, and the detection limit was 0.50 and 0.08 mg/L, respectively.     

Nitroso compounds : III. The reaction of bromomagnesium diphenylcuprate and phenylcopper reagents with nitrosobenzene

Bromomagnesium diphenylcuprate reagent reacts with nitrosobenzene to give diphenylhydroxylamine, biphenyl, diphenylamine, azoxybenzene and phenol. It reacts with alkyl nitrites to give the above products as well as the corresponding alkanols. Phenylcopper reagent behaves similarly but somewhat sluggishly. A mechanism involving an initial electron-transfer process is proposed.     

Synthesis of Nitroalkanes from Alkylhalides under Mild and Nonaqueous Conditions by Using Polymer Supported Nitrites

Alkyl halides are efficiently converted to their corresponding nitroalkanes under mild and nonaqueous conditions by using polymer supported nitrites. The polymeric reagent is regenerable.     

Simultaneous multiwavelength detection in flow injection analysis

The potential of the use of the diode-array detector in conjunction with flow injection analysis is outlined. Methods for multicomponent resolution can be based on the formation of complexes absorbing at different wavelengths. The example given is the determination of mixtures of copper(II) and iron(III) with a mixed 1:10-phenanthroline/neocuproine reagent. Amplification and dilution methods are based on the sum of the absorbances at several wavelengths and on monitoring absorbances at wavelengths away from the absorption maximum, respectively. The determination of nitrite via the Griess reaction is used as an example; the viable determination range is extended to 0.002/2-60.0 μg ml^?1 nitrite. Software for the implementation of the suggested methods is outlined.     

Reaction specificity of a titanium(IV)-porphyrin complex to hydrogen peroxide in view of an Ab initio study.

A Ti-TPyP reagent, i.e. an acidic aqueous solution of oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium(IV) complex, TiO(tpyp), was previously developed as a highly sensitive and specific reagent for determining hydrogen peroxide. In the present work, the reaction specificity of the TiO(tpyp) complex to hydrogen peroxide was clarified based on ab initio calculations. The results provide a well-grounded argument for determining hydrogen peroxide using the Ti-TPyP reagent experimentally.     

Determination of thiol groups with o-diacetoxy-iodobenzoate

o-Diacetoxyiodobenzoate is used for determining thiol groups by two procedures. In the first, thiols are titrated directly with the reagent at pH 6-8, with leuco-2,6-dichlorophenolindophenol and potassium iodide as indicator. In the second, thiols are treated at pH 7 with an excess of the reagent, the surplus being determined by reaction with excess of mercaptoacetic acid followed by back-titration of the latter with iodine. Both procedures yield results within 0.2% of the theoretical.     

Flow-injection determination of nitrites based on their reaction with thiocyanates

A technique for the flow-injection determination of nitrites with spectrophotometric signal detection was developed and studied. Additionally, a combination of the developed technique with the on-line pre-concentration of low concentrations of nitrites in surface and potable waters was investigated. The technique is based on the reaction of nitrites with thiocyanates. The product of the analytical reaction (nitroso-S-thiocyanate) and its adducts with strong acids are stable in aqueous solutions, which is supported by quantum chemical calculations. It is shown that the reaction chosen is attractive for analytical applications, because it is highly selective. A decrease in the detection limit down to 1.5 ng/mL (3s) is achieved by combining FIA with on-line ion-exchange preconcentration. The technique developed is used for monitoring nitrites in natural and waste water. The throughput capacity is 300 samples per hour.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 323–330.Original Russian Text Copyright © 2005 by Kuznetsov, Zemyatova, Ermolenko.     

Automated flow-injection spectrophotometric determination of nitrosamines in solid food samples

A spectrophotometric method using a flow-injection system is proposed for the determination of nitrosamines in foods (cured-meats). The method is based on the photochemical cleavage of the N-NO bond of the nitrosamine to yield the corresponding amine and nitrite. The nitrite is then detected spectrophotometrically, at 542 nm, by use of its reaction with a modified Griess reagent. Different linear ranges between 0.8 and 2000 ng mL(-1) are obtained for the method, depending on the time of exposure of the sample to the UV radiation. The relative standard deviation varies between 2.0 and 3.9% and the sample throughput is between three and seven samples per hour, depending on the experimental conditions. The proposed method was successfully applied to the analysis of N-nitrosodimethylamine in cured ham and loin, bacon, and sausages.     

无水浴砷铈催化光度法测定微量碘

对砷铈催化光度法这一微量碘的最常用测定方法进行了改进,取消了原方法中所有的水浴步骤,选用了更合适的反应器皿和反应终止剂,对试剂纯化进行了讨论,碘含量为０￣１０００μｇ／Ｌ的范围内,校正曲线的线性相关系数大于０．９９９。     

Nonaqueous diazotization of 5-amino-1-aryl-1H-pyrazole-4-carboxylate esters

5-Amino-1-aryl-1H-pyrazole-4-carboxylate esters are converted to the corresponding desamino, chloro, bromo, iodo, and methylthio esters by processes involving nonaqueous diazotization. Diazotizing agents are alkyl nitrites except in the case of chlorine where nitrosyl chloride is used. Evidence is presented that the latter reagent leads to the formation of cationic rather than radical intermediates.     

流动注射分光光度法测定亚硝酸盐仪器的研制

设计了亚硝酸盐流动注射自动在线监测仪,并研究了仪器的最佳测试条件．先将亚硝酸盐与对氨基苯磺酰胺重氮化,再与N-（1-萘基）乙二胺盐酸盐偶合,形成玫瑰红色的偶氮染料,在光程为60mm、光源为540nm的流通池内检测．实验发现最佳磺胺质量浓度为40g/L,N-（1-萘基）乙二胺盐酸盐质量浓度为0．6g／L,最佳采样量为300μL,反应管最佳长度为3m．亚硝酸盐的线性范围为10～1200μg／L,检出限为4．78μg／L,Rsd为1．02％（n=11）,实际水样的加标回收率在96．5％～106．2％之内．本仪器消耗试剂量少、测定快速、灵敏、抗干扰能力强,适宜于现场即时监测．     

Simultaneous ultrasound-assisted emulsification-derivatization as a simple and miniaturized sample preparation method for determination of nitrite in cosmetic samples by microvolume UV-vis spectrophotomety

A simple and miniaturized approach based on ultrasound-assisted emulsification-derivatization is proposed for the determination of nitrite in cosmetic samples by UV-vis micro-spectrophotometry. Oil/water emulsions were formed using 15 mg of cosmetic sample and 1 mL of an aqueous medium containing 0.5% w/v SDS and 1% v/v acetic acid. When powerful sonication systems were used to make emulsions, i.e. probe or cup-horn sonoreactor, stable and transparent emulsions were obtained in one or half minute per sample, respectively. The Griess reaction in these special conditions (i.e. sonication and the presence of an organized medium) was investigated. The absence of matrix effects allows external calibration with aqueous standards for nitrite quantification. Analytical features were compared to those of the European official method 82/434/EEC. Detection limit, sample throughput and reagent consumption were significantly improved.     

A Dip‐and‐Read Test Strip for the Determination of Nitrite in Food Samples for the Field Screening

Abstract

A new test strip method for field screening of nitrite in aqueous samples based on the diazo‐coupling reaction between the nitrite and the Griess reagents has been developed. The test strip has a circular sensing zone that contains two layers: the Griess reagents act as the sensing reagent and is immobilized in the bottom layer; the top layer is a cellulose acetate membrane that can be used as a dialysis membrane to remove the matrix from the sample, which can enhance the selectivity of this method. When the test strip was directly dipped into the samples, a color change of the test strip was observed, and the intensity of color that appears on the test strip is proportional to the concentration of nitrite in the range from 0.50 to 25 µg mL^?1 in food samples. Under the experimental conditions, as low as 0.20 µg mL^?1 nitrite can be observed; most of anionic and cationic species as well as other sample matrixes basically do not interfere with the nitrite measurement.     

Separation and Direct Chemical Determination of Nitrosamines by High Performance Liquid Chromatography (HPLC)

Abstract

Volatile and non-volatile nitrosamines are determined at subparts per million levels in a continuous, inexpensive, low-temperature procedure when samples are compatible with the aqueous-alcoholic solvents. Individual nitrosamines are resolved by gradient elution on appropriate HPLC columns, converted to nitrite ion by ultra-violet light, combined with modified Griess reagent and the red-colored product measured at 540 nanometers. Inorganic nitrite may be determined and two, organic compounds are known to interfere. The detection level for N-nitrosodimethyl amine is 0.1 parts per million.     

A highly sensitive method for the analysis of nitrite ions by capillary zone electrophoresis using water-soluble aminophenylporphyrin derivative as chromogenic reagent

The water soluble 5-p-aminophenyl)-10,15,20-tris(p-sulfonatophenyl) porphyrin, 4, acts as an extremely efficient chromogenic reagent for the detection of very low amounts of nitrites. The amino group of porphyrin 4 reacts smoothly with nitrite in acidic conditions 0.2 M HCl) producing the corresponding diazo-porphyrin derivative which is stable and does not show any appreciable hydrolysis to phenol within 6 h. The reaction is carried out in the presence of 25 mM heptakis-(2,6-di-O-methyl)-beta-cyclodextrin that prevents precipitation of the protonated form of porphyrins 4 or 5 due to the formation of strong inclusion complexes. The capillary zone electrophoresis of the diazoporphyrin and amino-porphyrin mixture shows severe peak tailing. However, symmetrical peaks can be obtained by adding 5 mM beta-cyclodextrin to the background electrolyte (20 mM phosphate buffer, pH 7.0). Calibration curve for nitrite analysis is linear up to 0.25 mM nitrite and the detection limit (at a signal-to-noise ratio of 3) has been estimated to be a 1 microM (50 ppb) of nitrite concentration in aqueous solutions.     

Chemometrics study of the kinetics of the Griess reaction

The kinetics of the Griess reaction in which 3‐nitroaniline acts as a nitrosation agent and 1‐naphtylamine as a coupling reagent was studied by chemometrics methods. The kinetic reaction was investigated under pH 1.0 and 25°C by UV‐vis spectrophotometry. The concentrations of nitrite, 3‐nitroaniline and 1‐naphtylamine were such that a second‐order kinetic reaction took place. Data explorations based on principal component analysis and multivariate curve resolution–alternating least squares were performed to obtain information about the reaction. Calculation of band boundaries of the multivariate curve resolution–alternating least squares solutions showed that the rotational ambiguities associated with the calculation of spectra and concentration profiles have been completely removed. The decrease in the ambiguity of the recovered solutions was closely related to the application of the equality constraint. The results of the exploratory data analysis showed that the kinetic reaction proceeds through a two‐step mechanism. Moreover, the two‐steps are second order. Data analysis approaches based on hard modeling and global hard modeling were used to resolve profiles of the reactants, intermediates and products and to evaluate the rate constants. Copyright © 2013 John Wiley & Sons, Ltd.     

Coupled multisyringe flow injection/reactor tank for the spectrophotometric detection of azinphos methyl in water samples

A multisyringe flow injection system with spectrophotometric detection is presented as a fast, robust and low-reagent consumption system for the determination of azinphos methyl (AzMe) in water samples. Determination is based on the Griess reaction. The analyte is hydrolyzed and the reaction product reacts with nitrite in acid medium to form the diazonium salt that reacts further with 1-naphtol reagent to produce an azo compound. The azo derivative is spectrophotometrically monitored at 485 nm. The influence of several chemical and flow variables has been investigated. Under the optimum analytical conditions, the linearity of the calibration curve for AzMe ranges from 1 to 32 μg mL^?1. The detection limit is 0.17?µg mL^?1, and recoveries between 95 to 109% have been obtained. The repeatability (RSD) is 0.8% for a 10?μg mL^?1 solution, and the injection throughput is seven samples h^?1. The system has been satisfactorily applied to the determination of AzMe in spiked river and dam water samples. The results were in agreement at the 95% confidence level with those obtained by HPLC.     

Determination of nickel(II) as the nickel dimethylglyoxime complex using colorimetric solid phase extraction

Colorimetric solid phase extraction (C-SPE) is an analytical technique in which analytes in water samples are extracted onto a solid adsorbent matrix impregnated with a colorimetric reagent and then quantified directly on the adsorbent surface using diffuse reflectance spectroscopy. This paper presents a further development in C-SPE. In this case, the reagent employed to detect the analyte is not impregnated on the extraction medium. Instead, the reagent is weakly immobilized on a solid support (i.e., filter paper) and released into the sample as it flows through the support. The reagent complexes the analyte in solution, forming a highly colored precipitate that is collected on the surface of an extraction membrane. The concentration of analyte is determined using the Kubelka-Munk function calculated from the diffuse reflectance spectrum of the precipitate on the membrane surface. This precipitation-spectrophotometric platform is extensively evaluated by determining nickel(II) using dimethylglyoxime (DMG) as the precipitating reagent. The ability to optimize reaction conditions with immobilized reagents by in-line buffering is also demonstrated. Specifically, borax buffer was utilized to adjust the pH of nickel(II) samples prepared in deionized water. This combination of immobilized buffer and reagent allows C-SPE to operate in a solid-phase mode in which all the reagents requisite for optimal analyte determination are immobilized on solid supports. Using this method, nickel(II) was determined in a single processing step over the concentration range 0.50-5.0 ppm in ∼40 s with 1.0 ml sample volumes.     

Azine Synthesis via Nitrogen-Nitrogen Bond Formation

Imine anions, generated by reaction of nitrites with organometallic reagents, are dimerized to form symmetrical azines through the use of CuI and t-butyl peroxybenzoate.