基于量子点增敏化学发光同时测定尿液中的亚硝酸盐和硝酸盐

采用铜镉柱还原硝酸盐,与CdTe量子点增敏过氧亚硝酸-碳酸钠体系的化学发光信号相结合,开发了快速在线同时分析亚硝酸盐和硝酸盐的新方法.对流动注射、化学发光等实验参数条件进行优化,在Na2CO3的浓度为0.2 M、H2O2的浓度为0.03 M、Na2EDTA的浓度为1×10-3 M、CdTe量子点粒径为2.84 nm的条件下,过氧亚硝酸-碳酸钠体系可以获得最优的化学发光信号.该方法检测亚硝酸盐的线性范围为0.3~75μM,检测限可达0.12μM,其相对标准偏差为1.9%;硝酸盐的线性范围为1.0~100μM,检测限可达0.26μM,其相对标准偏差为1.5%.此方法无需衍生和分离,可以实现同时、准确、快速和高选择性地检测人体尿液中亚硝酸盐和硝酸盐的含量,回收率分别为94%~105%和96.6%~110.4%.     

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.     

Simultaneous determination of nitrite and nitrate in human plasma by on-capillary preconcentration with field-amplified sample stacking

A simple method for the determination of nitrite and nitrate in human plasma has been developed using CZE with minimal sample preparation. Field‐amplified sample stacking (FASS) was used to achieve submicromolar detection by dilution of the plasma sample with deionized water. In CZE, the separation of nitrite and nitrate was achieved within 10 min without adding EOF modifier. The optimal condition was achieved with 50 mM phosphate buffer at pH 9.3. The ninefold diluted plasma samples were injected hydrodynamically for 40 s into a 60 cm×75 μm id uncoated fused‐silica capillary. The separation voltage was 20 kV (negative potential) and UV detection was performed at 214 nm. The linearity curves for nitrite and nitrate were obtained by the standard addition method. The estimated LODs for nitrite and nitrate in ninefold diluted plasma sample were 0.05 and 0.07 μM, respectively. The LODs for nitrite and nitrate in original plasma samples were 0.45 and 0.63 μM. The intra‐ and inter‐day precisions for both analytes were <2.6% and the recovery ranged between 92.3 and 113.3%. It was found that nitrite was more stable than nitrate in the plasma after the sample preparation. This proposed method was applied to a number of human plasma samples and the measured nitrite and nitrate concentrations in human plasma were consistent with the literature ranges.     

Enhanced Electrochemical Detection of Nitrite and Nitrite at a Cu-30Ni Alloy Electrode

ABSTRACT

Significant catalytic activity towards the reduction of nitrite at unmodified Cu - 30% Ni alloy electrodes was found within the concentration ranges 16 – 200 μM nitrite. The reduction of nitrite was found to occur at potentials significantly less negative than the reduction of nitrate thereby providing clear resolution and the possibility of reliable nitrite / nitrate speciation. The results are contrasted with those found at a bare copper electrode where the spatial resolution of the nitrate and nitrite reduction processes is severely limited with significant overlap of the reduction processes. The procedure represents an inexpensive and facile method for nitrite determination in a number of applications.     

Molecular emission cavity analysis: Part 23. Determination of Nitrite and Nitrate after Conversion to Nitrogen Monoxide

Molecular emission cavity analysis is applied to the determination of nitrite and nitrate after their reduction to nitrogen monoxide by iodide or zinc. The white emission stimulated from nitrogen monoxide in an oxy-cavity placed in a hydrogen—nitrogen diffusion flame is measured at 526 nm. Calibration graphs are linear up to 300 μg N ml^-1; the detection limit is 0.5 μg N ml^-1 for nitrite and 2 μg N ml^-1 for nitrate. There are few interferences. Procedures for the determination of nitrite and nitrate in admixture are described.     

Fluorimetric determination of nitrate in natural waters with 3-amino-1,5-naphthalenedisulphonic acid in a flow-injection system

A rapid, sensitive and precise flow-injection method for the determination of nitrate in natural waters is presented. Nitrate is first reduced in a copperized cadmium column to nitrite, which reacts with 3-amino-1,5-naphthalenedisulphonic acid to form the azoic acid. This acid forms a fluorescent salt in alkaline medium. The injecton rate is about 30 h^?1, the relative standard deviation for 10 injections of 2 × 10^?5 M nitrate is 0.8%, and the detection limit (S/N = 3)_is 1 × 10^?8 M nitrate.     

Sequential atomic absorption spectrometric determination of nitrate and nitrite in meats by liquid-liquid extraction in a flow-injection system

Sequential determinations of nitrate and nitrite based on continuous liquid-liquid extraction, and suitable for their routine determinations in meats, are reported. Nitrate reacts with bis(2,9-dimethyl-1,10-phenanthrolinato)copper(I) to form an ion-pair which is extrated into 4-methyl-2-pentanone in a flow-injection manifold. In one aliquot of sample, nitrite is oxidized by cerium(IV), so that total nitrate is determined. In another, nitrite is converted to nitrogen with sulfamic acid, so that only the original nitrate is determined. By measuring the atomic absorption signal of copper in the organic phase, mixtures of these anions can be determined at μg ml^?1 levels for nitrate/nitrite ratios from 10:1 to 1:10, with a sampling frequency of ca. 20 h^–1.     

Determination of traces of inorganic anions by means of high-performance liquid chromatography on zipaxsax columns

Zipax-SAX pellicular beads are used as the anion-exchanger material ; a high-pressure packing technique is described. A Zipax-SAX column (200 × 4.5 mm) is used in a separation system with eluent suppression and conductivity detection as in ion-chromatography. Good separation of chloride, nitrite, bromide, nitrate and sulfate is obtained with 1.4 × 10^-3 M succinate or adipate eluents at pH 7. A complete separation takes about 6 min at a flow rate of 3 ml min^-1. Detection limits of 2 μg l^-1 chloride, 4 μg l^-1 nitrate and 10 μg l^-1 sulfate can be reached if 2 ml of sample is preconcentrated.     

Membrane-dialzer injection loop for enhancing the selectivity of anion-responsive liquid-membrane electrodes in flow systems : Part 1. A sensing system for NOx and nitrite

A general approach for enhancing the selectivity of anion-responsive liquid-membrane electrodes is described. The method is based on use of the receptor channel of a flow-through dialyzer unit as the injection loop in a flow-injection system. An appropriate membrane in the dialyzer prevents ionic interferents from reaching an inselective electrode in the final flow stream. The concept is demonstrated by developing a highly selective semi-automated method for the determination of dissolved NO_x or nitrite at levels greater than 5 μM. Nitrogen dioxide is trapped across a teflon membrane in the dialyzer and converted to nitrate by a buffered peroxide recipient solution. This solution is injected and carried to a tubular nitrate electrode. The final selectivity and detection capabilities of this gas-sensing arrangement are examined and compared to those of the nitrate electrode alone and more conventional sensing systems based on pH electrodes. A dialyzer unit with wider channels improves the efficiency of gas transfer and thus the detection capabilities of the system.     

Spectrophotometric determination of trace nitrite based on catalytic oxidation of thionine by potassium bromate

A kinetic method for the determination of trace nitrite (7 × 10^?9–1.2 × 10^?6 M) based on its catalytic effect on the reaction between potassium bromate and thionine in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decreasing colour of thionine at 602 nm by the fixed-time method. At a given time of 5 min at 30°C, the detection limit is 2 × 10^?9 M (0.001 absorbance ratio, b = 1 cm) and the relative standard deviation for 1 × 10^?6 M nitrite is 2.6% (n = 6). The method is free from most interferences, especially from large amounts of nitrate. The procedure was successfully applied to the determination of trace nitrite in natural water and sausage samples without preconcentration and separation.     

Capillary electrophoresis determination of nitrate and nitrite in high-salt perchlorate solutions for the UC dissolution study

The capillary electrophoresis method with direct UV detection is proposed for the determination of nitrite and nitrate in high-salt perchlorate solutions issued from uranium carbide dissolution. The isotachophoretic sample stacking was used to compensate for the perchlorate matrix interference. Simple electrolyte composed of 120 mM formiate buffer, pH 3.8 enabled the nitrate and nitrite determination in the presence of up to 1000-fold excess of perchlorate with 2 μM and 4 μM detection limits for nitrate and nitrite, respectively. The proposed method was applied to the determination of nitrate and nitrite in high-salt non-irradiated uranium carbide dissolution samples.     

Simultaneous electrochemical determination of nitrate and nitrite in aqueous solution using Ag-doped zeolite-expanded graphite-epoxy electrode

In this work a new electrochemical sensor based on an Ag-doped zeolite-expanded graphite-epoxy composite electrode (AgZEGE) was evaluated as a novel alternative for the simultaneous quantitative determination of nitrate and nitrite in aqueous solutions. Cyclic voltammetry was used to characterize the electrochemical behavior of the electrode in the presence of individual or mixtures of nitrate and nitrite anions in 0.1 M Na₂SO₄ supporting electrolyte. Linear dependences of current versus nitrate and nitrite concentrations were obtained for the concentration ranges of 1-10 mM for nitrate and 0.1-1 mM for nitrite using cyclic voltammetry (CV), chronoamperometry (CA), and multiple-pulsed amperometry (MPA) procedures. The comparative assessment of the electrochemical behavior of the individual anions and mixtures of anions on this modified electrode allowed determining the working conditions for the simultaneous detection of the nitrite and nitrate anions. Applying MPA allowed enhancement of the sensitivity for direct and indirect nitrate detection and also for nitrite detection. The proposed sensor was applied in tap water samples spiked with known nitrate and nitrite concentrations and the results were in agreement with those obtained by a comparative spectrophotometric method. This work demonstrates that using multiple-pulse amperometry with the Ag-doped zeolite-expanded graphite-epoxy composite electrode provides a real opportunity for the simultaneous detection of nitrite and nitrate in aqueous solutions.     

荧光探针8-(3’,4’-二氨基苯)-二氟化硼-二吡咯甲烷用于光度法 灵敏测定食品中亚硝酸根和硝酸根

新型荧光探针8-(3’,4’-二氨基苯)-二氟化硼-二吡咯甲烷本体荧光很弱, 在酸性条件下, 和亚硝酸盐于30 ℃下反应15min后生成强荧光的三氮唑产物. 硝酸根可通过锌粉和氯化镉还原成亚硝酸根. 由此建立了一种新的荧光光谱法灵敏测定食品中的亚硝酸根和硝酸根. 其线性范围为0.06～6 μmol&#8226;L－1. 当信噪比等于3时, 方法的检出限为2 nmol&#8226; L－1. 将该方法首次用于多种食品中亚硝酸盐和硝酸盐的测定, 加标回收率为98.16%～103.20%.     

Reversed-phase ion-pair chromatographic method for the determination of nitroprusside in photolyzed solutions

A rapid reversed-phase ion-pair chromatographic method for disodium pentacyanonitrosylferrate(II) (nitroprusside) and its photodegradation products nitrite, nitrate, hexacyanoferrate(II) and hexacyanoferrate(III) is described. For chromatography, phenyl-bonded pellicular silica gel (10 μm) was used with a mobile phase consisting of water (0.005 M tetrabutylammonium phosphate, 0.0011 M n-octylamine, 0.01 M potassium dihydrogenphosphate, pH 7.0) and methanol (0.005 M tetrabutylammonium phosphate, 0.0011 M n-octylamine) (65:35); the detector was set at 220 nm. In 5% (w/v) dextrose solutions, the calibration graph for nitroprusside was linear over the concentration range 10–120 μg ml^?1. A qualitative explanation for the order of retention: hexacyanoferrate(II) < hexacyanoferrate(III) < nitroprusside is given. The method is suitable for the selective determination of nitroprusside in photolyzed infusion solutions (100 μg ml^?1 in aqueous 5% dextrose) and gives an impression of the decomposition products formed.     

Effect of transition metal chloride additives on the radiolysis of aqueous sodium nitrate

Radiolysis of aqueous sodium nitrate solution was studied as a function of concentration in the range 10^–4M to 1M NaNO₃. The radiolytic yield of nitrite was found to be linear with dose and concentration. The effect of transition metal chloride additives on the radiolysis of 0.01M NaNO₃ resulted in higher and lower yields of nitrite in the presence of cobalt and nickel chlorides, respectively, than that obtained in the pure nitrate system. The reduction of nitrate to nitrite is totally quenched even at very low concentration of copper chloride in the binary mixture. The results are explained on the basis of oxidizing and reducing properties of transition metal ions.     

Determination of Nitric Oxide-Derived Nitrite and Nitrate in Biological Samples by HPLC Coupled to Nitrite Oxidation

Nitrite and nitrate are main stable products of nitric oxide, a pivotal cellular signaling molecule, in biological fluids. Therefore, accurate measurement of the two ions is profoundly important. Nitrite is difficult to be determined for a larger number of interferences and unstable in the presence of oxygen. In this paper, a simple, cost-effective and accurate HPLC method for the determination of nitrite and nitrate was developed. On the basis of the reaction that nitrite is oxidized rapidly to nitrate with the addition of acidic potassium permanganate, the determination of nitrite and nitrate was achieved by the following strategy: each sample was injected twice for HPLC analysis, i.e. the first injection was to measure nitrate, and the second injection was to measure total nitrate including initial nitrate and the nitrate from the conversion of nitrite with the addition of acid potassium permanganate in the sample. The amount of nitrite can be calculated as difference between injections 2 and 1. The HPLC separation was performed on a reversed phase C₁₈ column for 15 min. The mobile phase consisted of methanol–water (2:98 by volume); the water in the mobile phase contained 0.60 mM phosphate salt (potassium dihydrogen and disodium hydrogen phosphate) and 2.5 mM tetrabutylammonium perchlorate (TBAP). The UV wavelength was set at 210 nm. Additionally, we systemically investigated the effects of the concentration of phosphate salt and TBAP in the mobile phase, the pH of the mobile phase, and the amount of acidic potassium permanganate added to the sample on the separation efficacy. The results showed that the limits of detection (LOD) and the limit of quantitation (LOQ) were 0.075 and 0.25 μM for nitrate (containing the oxidized nitrite), respectively. The linear range was 1–800 μM. This developed approach was successfully applied to assay nitrite/nitrate levels in cell culture medium, cell lysate, rat plasma and urine.

     

A novel spectrofluorimetric method for the ultra trace analysis of nitrite and nitrate in aqueous medium and its application to air, water, soil and forensic samples

A highly sensitive and virtually specific method has been developed for the trace and ultra trace 5 ng ml⁻¹-1 μg ml⁻¹ fluorimetric analysis of nitrite. The method is based on the quenching action of nitrite on the native fluorescence of murexide (ammonium purpurate) [λ_ex=349.0 nm, λ_em=444.5 nm] in the acid range of 0.045-0.315 (M) H₂SO₄. The method is very precise and accurate (S.D.=±0.4877 and R.S.D.=0.4878% for the determination of 0.1 μg ml⁻¹ of nitrite in 11 replicates). Relatively large excesses of over 35 cations and anions do not interfere. The proposed technique has been successfully applied for the determination of nitrite and nitrate in ground water, surface water and sea water, nitrite in soil and nitrate in forensic samples. The method has also been extended for the analysis of NO_x in air.     

Determination of Nitric Oxide-Derived Nitrite and Nitrate in Biological Samples by HPLC Coupled to Nitrite Oxidation

Nitrite and nitrate are main stable products of nitric oxide, a pivotal cellular signaling molecule, in biological fluids. Therefore, accurate measurement of the two ions is profoundly important. Nitrite is difficult to be determined for a larger number of interferences and unstable in the presence of oxygen. In this paper, a simple, cost-effective and accurate HPLC method for the determination of nitrite and nitrate was developed. On the basis of the reaction that nitrite is oxidized rapidly to nitrate with the addition of acidic potassium permanganate, the determination of nitrite and nitrate was achieved by the following strategy: each sample was injected twice for HPLC analysis, i.e. the first injection was to measure nitrate, and the second injection was to measure total nitrate including initial nitrate and the nitrate from the conversion of nitrite with the addition of acid potassium permanganate in the sample. The amount of nitrite can be calculated as difference between injections 2 and 1. The HPLC separation was performed on a reversed phase C₁₈ column for 15 min. The mobile phase consisted of methanol–water (2:98 by volume); the water in the mobile phase contained 0.60 mM phosphate salt (potassium dihydrogen and disodium hydrogen phosphate) and 2.5 mM tetrabutylammonium perchlorate (TBAP). The UV wavelength was set at 210 nm. Additionally, we systemically investigated the effects of the concentration of phosphate salt and TBAP in the mobile phase, the pH of the mobile phase, and the amount of acidic potassium permanganate added to the sample on the separation efficacy. The results showed that the limits of detection (LOD) and the limit of quantitation (LOQ) were 0.075 and 0.25 μM for nitrate (containing the oxidized nitrite), respectively. The linear range was 1–800 μM. This developed approach was successfully applied to assay nitrite/nitrate levels in cell culture medium, cell lysate, rat plasma and urine.     

Preparation of Pt/MWCNTs Catalyst by Taguchi Method for Electrooxidation of Nitrite

Abstract—The Pt nanoparticles-functionalized multiwall carbon nanotubes (f-MWCNTs) modified glassy carbon electrodes were used to study the electrooxidation of nitrite. Pt nanoparticles were electrodeposited on the f-MWCNTs modified glassy carbon (GC) electrode by applying a constant potential to the electrode for a specific time. By applying optimized conditions (using Minitab software), Pt/MWCNTs/GC electrode was prepared by immobilizing 40 μL of f-MWCNTs on the GC electrode and applying a potential of–0.20 V vs. Ag/AgCl for 120 s. The electrooxidation of nitrite was studied on the prepared electrode in 0.1 M KCl solution. The amperometric response of the prepared electrode linearly changes with the concentration of nitrite from 4.0 μM to 2.4 mM. The detection limit of the electrode was found to be 1.5 μM (S/N = 3) with a sensitivity of 28.7 μA/mM.     

Simultaneous determination of nitrate and nitrite by flow injection analysis

An automatic method for the simultaneous determination of nitrate and nitrite by flow injection analysis is described. Nitrate is reduced to nitrite with a copperized cadmium column. Nitrite is diazotized and coupled with N-(l-naphthyl)ethylenediammonium dichloride. The merging zones approach is used to minimize reagent consumption. The injector system is arranged so that two peaks are obtained, one corresponding to nitrite and the other to nitrite plus nitrate. A sampling rate of about 90 samples per hour is possible; the precision is better than 0.5% for nitrite in the range 0.1–0.5 mg l^t and 1.5% for nitrate in the range 1.0–5.0 mg l^t