Sequential flow injection spectrophotometric determination of nitrite and nitrate in various samples

Catalytic simultaneous spectrophotometric determination of nitrite and nitrate with a flow injection system

A simple efficient and practical separation/preconcentration coupled with HPLC method for the determination nitrate and low concentrations of nitrite in human urine and blood was investigated. The method is based on precolumn derivatization using the Griess reaction and cloud-point extraction (CPE) of nitrite anion and direct determination of nitrate using its UV absorbance by ion-pair HPLC. The chromatographic process with detection at two wavelengths (510 and 220 nm) allows the determination of nitrite and nitrate. Decolorization and protein precipitation of urine and blood was applied to overcome the interference of matrix and enhance the sensitivity. The method was validated for linearity, accuracy and precision. Under the optimum conditions, the linear range of nitrite from 10 to 1,000 ng/mL and nitrate from 0.1 to 10 µg/mL. Product recoveries ranged from 92.4 to 99.9%. The limits of detection were 1 ng/mL and 0.1 µg/mL for nitrite and nitrate, respectively. Therefore, the technique was simple and reliable, with potential application in biological sample analysis of nitrate and nitrite.

Borax, salicylic acid, nitrite, and nitrate have been used as food additives during processing for preserving, coloring, and stabilizing food. These four chemical food additives impact consumer health, e.g., liver cancer and gastric cancer. To maintain the high quality of food and to comply with food safety, a paper-based analytical device (PAD) coupled with a colorimetric method is proposed to simultaneously determine these four chemical food additives in this work. The Griess reaction can be used for the determination of nitrite, and nitrate was reduced to nitrite on the PAD in the section with a hydrophilic channel coated with zinc dust prior to detection by the Griess reaction. Borax and salicylic acid were determined using the complexation reactions with curcumin and FeCl₃, respectively. This work presents the development of colorimetric methods on a PAD for the simultaneous determination of borax, salicylic acid, nitrite and nitrate in food samples. Limits of detection were (mg/L) 10 for borax, 35 for salicylic acid and 0.4 for nitrite and nitrate. Our PAD with a colorimetric method was also used for the determination of borax, salicylic acid, nitrite and nitrate in real food samples. Our detection limits were 3−5 times lower than those of commercial test kits, and the results from the real food samples were not statistically significantly different from those obtained via UV-Vis spectrophotometry at the 95% confidence level (t-test paired samples). Our proposed PAD can rapidly determine four chemical food additives in food with a high sensitivity and is an instrument-free technique.

Simple flow-injection system for the simultaneous determination of nitrite and nitrate in water samples

The research aims to design a new flow injection system using the two continuous and successive techniques for the determination of cerium quaternary, through the interaction of cerium quaternary with potassium iodide in an acidic medium and the liberation of yellow-colored iodine, which gives a maximum absorption peak at the wavelength is 353 nm. The method includes manufacturing a quadruple valve from cheap materials and choosing the optimal system design with studying the optimal conditions for the system, which include potassium iodide concentration, acid concentration, Pump speed, acid volume, pattern size, reaction profile length, then designing a new sequential injection system and selecting the optimal design for it. The flow injection method yielded compliance with Beer-Lambert law in the range (1-40 mg/L). And a correlation coefficient (R2) of 0.997, and a dilution coefficient equal to 1.33 and 1.32 for concentrations of 10 and 30 mg / L, respectively. The sequential injection method also gave a clear improvement in the height of the apex and an increase in sensitivity.

Simultaneous flow injection determination of nitrate and nitrite in water by gas-phase chemiluminescence

Simultaneous spectrophotometric determination of nitrite and nitrate in a flow-injection system

A method for the determination of trace amounts of arsenic in food samples using flow injection analysis and atomic absorption spectrometry with hydride generation (FI-HG AAS) was developed. The parameters of the flow injection system and the hydride generation were optimized with respect to reagent concentrations, atomization temperature, injection volume, reaction coil length and carrier flow rate. The limits of detection and quantification were 0.34 µg L−1 and 1.2 µg L−:1, respectively, and the analytical curve is linear up to 30.0 µg L−1 arsenic. The relative standard deviation for 12 replicates varies between 5% for 4.0 µg L−1 As and 1.8% for 30.0 µg L−1 As, with an injection frequency of up to 135 h−1. Interferences from Ni(II), Cu(II), Fe(III), Cr(III), Mo(II), Bi(III), Se(IV), Se(VI), Sb(III) and Sb(V) could be masked with a mixture of ascorbic acid-KI in a 5.0 mol L−1 HCl solution. The accuracy of the proposed method was evaluated by using certified reference materials of biological samples, and the method was used to determine the content of arsenic in fish and coffee beans.

Nitrogen speciation by microstill flow injection analysis

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.

Detection of amino acids at conducting electroactive polymer modified electrodes using flow injection analysis. Part II. Use of microelectrodes

A method is reported for improved accuracy for nitrate and nitrite determinations in aqueous solutions, especially plant extracts. The sampling procedure can be adapted for automated determinations: At least 6 aliquots with increasing volume of nitratecontaining solutions are subjected to the reducing agent under stabilized conditions to obtain nitrite, treated with one of 2 different diazotization reagents, and measured colorimetrically. The slope of the curve, absorbance vs sampled volume, is determined by linear regression; this slope is directly dependent on the nitrate (nitrite) content. Original nitrite is determined by omitting the reducing step. Low nitrate levels (<0.1 μg/mL) can be determined directly with the sulfanilamide-N-(l-naphthyl)ethylenediamine dihydrochloride diazotization procedure or indirectly by constant nitrate addition, with the sulfanilic acid-1-naphthylamine hydrochloride diazotization mixture (Griess reagent). The latter procedure can be used to measure concentrations up to20μg/mL.

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.

A method was developed for determination of arsenic by Atomic Absorption Spectrometry - Hydride Generation in Flow Injection Analysis (FIA). The flow injection system was operated in the merging zones configuration, where sample and reagent are simultaneously injected into two carrier streams, HC1 and H2O, respectively. For separation of arsine a continuous gas-liquid separator was designed. The liquid phase flows to a free-running drain while the gaseous phase is purged by nitrogen into the atomization cell. The optimum conditions for the generation of arsine were established as: reaction coil of 50 cm, sample and reagent injected volume of 250 p.L, 1.0% (m/v) solution of sodium tetrahydroborate and 1.0 mol L’1 hydrochloric acid, cell temperature of 900°C, flow rates of 3.6 mL min’1 for hydrochloric acid and tetrahydroborate Solutions and a flow rate of 130 mL min-1 for the carrier gas (N2). Many elements cause interferences in this technique in gaseous and condensed phases. It was found that Mn(II), Pb(Il), Fe(IIl), Cu(II), Ni (II), Zn (II), Al (III) and Cd (II) caused signal reductions for arsenic of at least 10%. The interferences were reduced by using an on-line mini-column with 50 mg of the cation exchange resin Amberlite IRA-120. The interferences in the gaseous phase were caused by Se(IV), Sn(II), Sb(III), Bi(III) and Te (IV). To overcome these efíects, thioureia was used as masking agent. Under the optimum experimental conditions, the detection limit. defined as three times the standard deviation of the blank measurement, was found to be 0,35 ng mL’1 for As(lII) and 0,52 ng mL’1 for As(V). The relative standard deviation of 2,3% for 0,1 mg L’1 As(IIl) and 1,7% for 0,1 mg L’1 As(V) and a sampling rate of about 120 determinations per hour. The method was shown to be satisfactory for determination of traces arsenic in water samples (natural and certificate).

Pyoverdin, a natural fluorescent pigment biosynthesized by Pseudomonas fluorescence, was entrapped in sol–gel glass and used as a reactive solid phase for the determination of trace amounts of FeIII. No leaching or bleaching of the trapped reagent was observed. The fluorescent siderophore was more stable in sol–gel glass than on controlled-pore glass. Iron(III) was determined by continuous flow and flow injection (FI) methods. Both methods provided a fast response. The detection limits were 3 ng ml–1(relative standard deviation, 3.0% for 150 ng ml–1 of FeIII) and 20 ng ml–1(relative standard deviation, 4.5% for 500 ng ml–1 of FeIII) for the continuous and FI (sample injection 1 ml) systems, respectively. The selective sensor was successfully used to determine iron in tap waters (continuous system) and human serum (FI system).