Nitrite In Natural Water Samples Research Articles

On-site detection of nitrate plus nitrite in natural water samples using smartphone-based detection

Nitrate plays an important role in the nitrogen cycle and is also a known pollutant of the aquatic ecosystem. Rapid, sensitive, and on-site analysis of nitrate is helpful for biogeochemical study of nitrogen and evaluation of water quality. In this study, a simple green manual method based on the VCl3 reduction-Griess reaction was established for nitrate analysis. The effects of reaction parameters including temperature, reagent concentration, salinity, and nitrite content on nitrate determination were comprehensively evaluated and optimized using a standard laboratory spectrophotometer. This method exhibited a detection limit of 0.15 μmol L−1, relative standard deviations of less than 1%, and an analytical range as high as 60 μmol L−1 before dilution. As many as 20 samples were measured within 1 h. Different natural water samples (n = 60) with various salinities were measured with excellent accuracy (<3% error) and high recovery (94–105%). Real on-site detection was achieved using smartphone-based detector. There was a good linear relationship between the intensity of green channel and the concentration of nitrate up to 20 μmol L−1 (R2 = 0.9988). There is no significant difference of detection results between spectrophotometer and smartphone in practical application (t-test, p = 0.97 > 0.05). The proposed method is salinity-interference-free, robust, and easy-to-operate, which make it suitable for both laboratory routine and on-site analysis.

Electrochemical preparation of gold nanoparticles on ferrocenyl-dendrimer film modified electrodes and their application for the electrocatalytic oxidation and amperometric detection of nitrite

This work describes the preparation of sensors for electrochemical determination of nitrite, based on modified electrodes prepared by simple and reliable electrodeposition methods. Glassy carbon and platinum electrodes were modified with composite films made from gold nanoparticles (AuNPs) and a carbosilane-dendrimer possessing peripheral electronically communicated ferrocenyl units (Dend), using potentiostatic and cycling techniques. AuNPs with diameters in the range 12–24nm were assembled to form fractal and flowerlike structures on the surface of electrodes. The modified electrodes exhibited remarkable electrocatalytic activity toward the oxidation of nitrite giving higher peak currents at lower oxidation overpotentials than those found for the bare electrode and the dendrimer-modified electrode. The voltammetric study showed that the electrochemical oxidation of nitrite involves one-electron in the rate-determining step reaction. It is proposed that the mechanism for the interaction of nitrite with ferrocene groups to be oxidized involves attachment to the ferrocene center. At the AuNPs it is possible to consider that the oxidation of NO2− to NO2 probably proceeds through an adsorption stage. The heterogeneous rate constant, k, for the oxidation of nitrite at the surface of the modified electrodes was determined by rotating disk electrode voltammetry using Koutecky–Levich plots. The transfer coefficients for electrocatalytic oxidation of nitrite under the experimental conditions were also investigated in this study. Under the optimum conditions the sensor has a linear response in the 10μM to 5mM concentration range, a high sensitivity of 44.8μAμM−1, and a low detection limit of 2.0×10−7M. Most common ions do not cause interferences. The sensor was successfully applied to the determination of nitrite in natural water samples.

Chemiluminescence study of carbonate and peroxynitrous acid and its application to the direct determination of nitrite based on solid surface enhancement

Peroxynitrous acid (ONOOH) was produced by the on-line mixing of acidified hydrogen peroxide with nitrite in a flow system. A strong chemiluminescent (CL) emission was observed when ONOOH reacted with carbonate without any special CL reagents. When cotton was present in the CL cell, the CL emission was enhanced significantly. The method was developed to determine nitrite, which showed a key improvement that any CL reagents and sensitizers were not used, resulting in better selectivity. The applicability of the present CL system was demonstrated for the sensitive and selective determination of nitrite in natural water samples without any special pretreatment. Good agreements were obtained for the determination of nitrite in tap and well waters between the present approach and a standard spectrophotometric method. The average precision was 4.6% ( n=7) and detection limit ( S/ N=3) was 1.0×10 −7 M. Based on the CL spectrum, UV spectra, and dissolved oxygen measurement, a possible CL mechanism was proposed. ONOOH was an unstable compound in acidic solution and could be quenched into peroxynitrite (ONOO −) in basic solution. ONOO − reacted with CO 2 to produce ONOOCO 2 −, which can rapidly decompose into NO 2 and CO 3 − radicals. In the presence of H +, CO 3 − radicals can protonate to bicarbonate radical (HCO 3 ). The recombination of HCO 3 radicals and decomposition can lead to light emission.

Corn leaf nitrate reductase--a nontoxic alternative to cadmium for photometric nitrate determinations in water samples by air-segmented continuous-flow analysis.

Development, characterization, and operational details of an enzymatic, air-segmented continuous-flow analytical method for colorimetric determination of nitrate + nitrite in natural-water samples is described. This method is similar to U.S. Environmental Protection Agency method 353.2 and U.S. Geological Survey method 1-2545-90 except that nitrate is reduced to nitrite by soluble nitrate reductase (NaR, EC 1.6.6.1) purified from corn leaves rather than a packed-bed cadmium reactor. A three-channel, air-segmented continuous-flow analyzer-configured for simultaneous determination of nitrite (0.020-1.000 mg-N/L) and nitrate + nitrite (0.05-5.00 mg-N/L) by the nitrate reductase and cadmium reduction methods-was used to characterize analytical performance of the enzymatic reduction method. At a sampling rate of 90 h(-1), sample interaction was less than 1% for all three methods. Method detection limits were 0.001 mg of NO2- -N/L for nitrite, 0.003 mg of NO3-+ NO2- -N/L for nitrate + nitrite by the cadmium-reduction method, and 0.006 mg of NO3- + NO2- -N/L for nitrate + nitrite bythe enzymatic-reduction method. Reduction of nitrate to nitrite by both methods was greater than 95% complete overthe entire calibration range. The difference between the means of nitrate + nitrite concentrations in 124 natural-water samples determined simultaneously bythe two methods was not significantly different from zero at the p = 0.05 level.

A kinetic method for the determination of nitrite by its catalytic effect on the oxidation of chlorpromazine with nitric acid.

A catalytic spectrophotometric method for the determination of trace amounts of nitrite is proposed. In acidic solution, chlorpromazine (CP) is oxidized by nitric acid to form a red compound, which is further oxidized to a colorless compound. The reaction is accelerated by trace amounts of nitrite and can be followed by measuring the absorbance at 525 nm: nitrite ion is regenerated and multiplied by nitric acid. The absorbance of the reaction increased with an increase in the reaction time, reached a maximum and decreased rapidly. Since the time required for the absorbance to reach the maximum decreased with increasing nitrite concentration, this value was used as the measured parameter for the nitrite determination. Under the optimum experimental conditions (2.3 M nitric acid, 1.2 x 10(-5) M CP, 40 degrees C), nitrite can be determined in the range 0-100 microg l(-1). The relative standard deviations (n = 6) are 4.7 and 1.8% for 40 and 100 microg l(-1) nitrite, respectively. The detection limit of this method (3sigma) is 1.2 microg l(-1). This method was successfully applied to a determination of nitrite in natural water samples.

Spectrophotometric determination of nitrate and nitrite in natural water samples based on an oxime formation reaction of phenol.

The spectrophotometric method for the determination of nitrate reported by Velghe and Clays was modified.The modified method was applied to the determination of nitrate and nitrite in natural water samples(well, river, and seawater).In the modified method, a sodium chloride solution was used instead of hydrohloric acid as the source of chloride for reducing nitrate.The sensitivity of this method was comparable to that of ion chromatography and that of HPLC with UV detection.The results obtained by the proposed method were in good agreement with those obtained by the chromatographic methods.The proposed method could be applied to the determination of nitrate of low concentration levels in seawater sample.

Reverse Polarity Capillary Zone Electrophoretic Analysis of Nitrate and Nitrite in Natural Water Samples

This paper describes the application of reverse polarity capillary zone electrophoresis (CZE) for rapid and accurate determination of nitrate and nitrite in natural water samples. Using hexamethonium bromide (HMB) as an electroosmotic flow modifier in a borate buffer at pH 9.2, the resolution of nitrate and nitrite was accomplished in less than 3 min. CZE was compared with ion chromatographic (IC) and cadmium reduction flow injection analysis (Cd-FIA) methods which are the two most commonly used standard methods for the analysis of natural water samples for nitrate and nitrite. When compared with the IC method for the determination of nitrate and nitrite, CZE reduced analysis time, decreased detection limits by a factor of 10, cut laboratory wastes by more than 2 orders of magnitude, and eliminated interferences commonly associated with IC. When compared with the cadmium reduction method, CZE had the advantage of simultaneous determination of nitrate and nitrite, of being able to be used in the presence of various metallic ions that normally interfere in cadmium reduction, and of decreased detection limits by a factor of 10.

Primaquine Phosphate as a Promising Substitute for N-(l-Naphthyl)ethylenediamine I. Determination of Nitrite in Natural Waters in Egypt

A sensitive and rapid colorimetric method was developed for the determination of nitrite in natural water samples. The method is based on coupling primaquine phosphate (PP) with diazotized p-nitroaniline (PNA) or with diazotized p-aminobenzophenone (PABP) in acid medium. The orange color produced with both amines was stable for more than 24 h, and has an absorption maximum at 484 nm, and 482 for PNA and PABP, respectively. The calibration graph was linear in the concentration range of 0.025–1.25 ppm of nitrite, with a minimum detection limit of 0.015 ppm. The molar absorptivities were 8×104 mol-1 cm-1 and 7.11×104 mol-1 cm-1 for PNA and PABP, respectively. Heavy metals common to natural waters did not interfere. The interference from reducing anions such as I”, S2-, SO32-, and S2O32- was eliminated by precipitation as insoluble lead salts. The excess lead ions did not interfere. Because PP is less liable to self-diazotization-coupling reaction compared with N-(l-naphthyl)ethylenediamine (BMR), the method could be adopted for automated flow-injection analysis of nitrite. In addition, the coupling agent used is safe; a promising substitute for the so-long used Bratton-Marshal reagent which was reported to be carcinogenic. The proposed method is very sensitive and selective.

Spectrophotometric Determination of Nitrite Based on Its Catalytic Effect on the Oxidation of 2,2′-Azinobis(3-ethylbenzothiazoline-6-sulfonic acid)

A kinetic method for the spectrophotometric determination of a micro amount of nitrite in natural water was developed with 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ARTS) by batchwise and flow-injection techniques. ABTS is oxidized by nitrite in an acidic medium beyond the amounts of stoichiometric completion. The nitrite in each sample was determined by relationship between the absorbance or the peak height and the concentration of standard nitrite solution. By both methods, 10 ppb levels of nitrite can be determined. The main drawback of the proposed method involves severe interference due to oxidizing cations. These cations could be effectively removed by the introduction of an ammonium form cation-exchange resin. By using the batchwise method, the relative standard deviation for 10 measurements of 100 ppb nitrite was 1.2%, The procedures have been applied successfully to the determination of nitrite in natural water samples, such as rain water.

Studies on the application of photochemical reactions in a flow injection system. Part 1. Determination of trace amounts of nitrite, based on its inhibitory effect on the photochemical reaction between iodine and ethylenediaminetetraacetic acid

An automated procedure for the photochemical determination of nitrite has been developed, involving use of a laboratory-built flow-through photochemical reactor and a laboratory-built flow-through amperometric detector in a flow injection system, based on the inhibitory effect of nitrite on the photochemical reaction between iodine and ethylenediaminetetraacetic acid. Optimum analytical conditions were established. Nitrite can be determined in the range from 1 × 10–7 to 4 × 10–6 mol dm–3, with a sampling frequency of 60–80 h–1 and a relative standard deviation of less than 1%. The method has been applied to the determination of nitrite in natural water samples, and recoveries of at least 91% have been attained.