Rapid Analysis of Nitrate and Nitrite by Ion-Interaction Chromatography on a Monolithic Column

Ion-interaction chromatography with direct conductivity detection has been used for analysis of nitrate and nitrite. Chromatographic separation was performed on a monolithic silica-based C₁₈ column dynamically modified with tetrabutylammonium (TBA⁺). Using the optimized mobile phase, containing 2.0 mmol L^?1 TBA⁺ and 0.8 mmol L^?1 citrate (pH 6.0), delivered at a flow rate of 6.0 mL min^?1, separation of five anions (chloride, nitrite, bromide, nitrate, and sulfate) was achieved in only 40 s at a column temperature of 30 °C. The detection limits for nitrate and nitrite were 0.74 and 0.92 mg L^?1, respectively. The relative standard deviation (RSD, n = 5) of the retention times of nitrate and nitrite was 0.1% and RSD of chromatographic peak areas were 0.4 and 0.2%, respectively. The method was successfully used for analysis of the anions in groundwater. Recovery of nitrate and nitrite was 99.1 and 105%, respectively.     

An Addition Method for the Direct Ultraviolet Spectrophotometric Determination of Nitrite in the Presence of a Large Excess of Nitrate

Abstract

The ultraviolet spectra of aqueous nitrite and nitrate solutions and of binary mixtures were obtained. By using an addition technique and a reference nitrate/nitrite solution it was possible to compensate for the interference caused by the overlapping of the nitrate and nitrite bands, which is normally a limiting factor in the analysis of mixtures of nitrite with large excesses of nitrate. The detection limit was 5 × 10^?5 M NO₂ ^? which corresponded to a minimum detectable amount of 2.3 ppm NO₂ ^? in the presence of up to 20,000 times greater amount of NO₃ ^?. The accuracy was ± 0.6% and the standard deviation ± 0. 002.     

Denitrification of simulated nitrate-rich wastewater using sulfamic acid and zinc scrap

An enhanced chemical denitrification process was studied as an alternative treatment of nitrate-rich wastewater which cannot be easily treated using conventional biological methods. To accelerate denitrification and to reduce the conversion to ammonia, nitrite reductants were added. In a batch test with the initial nitrate concentration of 500 mg NO ₃ ^? -N per L, sulfamic acid and zinc were found to be the best nitrite and metal reductants, respectively. In a column test with the initial nitrate concentration of 500 mg NO ₃ ^? -N per L, optimum results were experimentally obtained over a zinc scrap column with a 1.0 molar ratio of [NH₂SO₃H]/[NO ₃ ^? -N] and the recirculating flow rate of 6 L min^?1 at pH 2.5. Approximately 98.8 % of nitrate anions were removed, and the observed reaction rate constant (k) was 0.135 min^?1. Zinc consumption was reduced to 46.6 % compared to the procedure without sulfamic acid, and sulfamic acid consumption was reduced to 40 % compared to the results of our previous study. Based on these experimental results, it was concluded that chemical nitrate denitrification using sulfamic acid and zinc scrap is an effective alternative treatment protocol for nitrate-rich wastewater.     

Diaminobenzene as a Novel Reagent for Nitrite Assay in Environmental Samples: Evidence for Its Mechanistic Aspects

Abstract

o-Phenylenediamine has been used as a reagent to quantify nitrites/nitrates in a variety of sample matrices. The method is based on the cyclization reaction between o-phenylenediamine and nitrite in acid medium. The amine undergoes diazotization with nitrite in the presence of acid to form the diazonium ion, which subsequently cyclizes to yield yellowish orange benzotriazole at room temperature with an absorption maximum at 450 nm. The formed dye has been separated, purified, and characterized by IR, NMR, and spectroscopy techniques. The parameters of the reaction between amine and nitrite have been optimized. The effect of interfering ions on the determination of nitrites/nitrates has been described. The developed method has been applied for the determination of residual NO₂ gas present in the ambient air after fixing it as a nitrite ion using sodium arsenite as a trapping medium. The dye formed has been extracted into organic solvent to improve the detection limit during the measurement of low levels of ambient NO₂ in air. The method obeyed Beer's law in the concentration range 0–250 µg in aqueous medium and 0–50 µg in organic medium with molar absorptivity of 4.09 × 10⁴ L mol^?1 cm^?1 and 4.3 × 10⁴ L mol^?1 cm^?1 respectively. Nitrate is determined by reducing it to nitrite after passing through the copperized cadmium reductor column. The developed method has been applied to determine nitrite/nitrate levels in water, soil, and biological samples.     

Determination of Total Nitrogen in Environmental Samples: Validation by Comparison of Techniques and Intralaboratory Studies

Abstract

A rapid, microwave-based extraction method was employed to oxidize all forms of nitrogen to nitrate in environmental samples using persulfate. The digest was then analyzed spectrophotometrically after an offline reduction of nitrate to nitrite using a cadmium reductor column was completed. The precision of the method was tested at the 0.5 mg l^?1 level and was 5.2% (N = 10). The detection limit based on S/N = 3 was calculated to be 0.15 mg l^?1. The method was thoroughly validated by comparison of analytical techniques and intralaboratory comparison studies.     

Kinetics and products of the gas-phase reactions of the OH radical and O3 with allyl chloride and benzyl chloride at room temperature

The kinetics of the gas-phase reactions of allyl chloride and benzyl chloride with the OH radical and O₃ were investigated at 298 ± 2 K and atmospheric pressure. Direct measurements of the rate constants for reactions with ozone yielded values of ??(O₃ + allyl chloride) = (1.60 ± 0.18) × 10^?18 cm³ molecule^?1 s^?1 and ??(O₃ + benzyl chloride) < 6 × 10^?20 cm³ molecule^?1 s^?1. With the use of a relative rate technique and ethane as a scavenger of chlorine atoms produced in the OH radical reactions, rate constants of ??(OH + allyl chloride) = (1.69 ± 0.07) × 10^?11 cm³ molecule^?1 s^?1 and ??(OH + benzyl chloride) = (2.80 ± 0.19) × 10^?12 cm³ molecule^?1 s^?1 were measured. A study of the OH radical reaction with allyl chloride by long pathlength FT-IR absorption spectroscopy indicated that the co-products ClCH₂CHO and HCHO account for ca. 44% of the reaction, and along with the other products HOCH₂CHO, (ClCH₂)₂CO, and CH₂ ? CHCHO account for 84 ± 16% of the allyl chloride reacting. The data indicate that in one atmosphere of air in the presence of NO the chloroalkoxy radical formed following OH radical addition to the terminal carbon atom of the double bond decomposes to yield HOCH₂CHO and the CH₂Cl radical, which becomes a significant source of the Cl atoms involved in secondary reactions. A product study of the OH radical reaction with benzyl chloride identified only benzaldehyde and peroxybenzoyl nitrate in low yields (ca. 8% and ?4%, respectively), with the remainder of the products being unidentified.     

Determination of Atenolol in Human Plasma by Pseudo Reversed Phase Liquid Chromatography-Tandem Mass Spectrometry

Previous HPLC determination of atenolol on reversed-phase packings has often required a mobile phase containing three components: organic modifier, buffer and ion-pairing reagent or organic amine. In addition to the complexity of the eluents employed, alkyl sulphonates and organic amines in the mobile phase can reduce the life of silica-based bonded columns. A new simple, rapid and sensitive method—pseudo reversed-phase liquid chromatography/tandem mass spectrometry has been developed for the analysis of atenolol in human plasma using bare silica as the stationary phase coupled with a simple mobile phase consisted of 5% acetonitrile and 95% formate buffer. The optimization of separation is fast and easy. The assay was validated for the concentration range 1–100 ng mL^?1 with a detection limit of 1 ng mL^?1. Moreover, the silica column was durable with the mainly aqueous eluents. No obvious loss in performance was observed for 30,000 column volumes of eluent.     

Denitrification and removal of heavy metals from waste water by immobilized microorganisms

Pseudomonas fluorescens, immobilized on soft polyvinyl chloride granules containing up to 35% softeners as carbon source, was used for simultaneous removal of nitrate and heavy metals. In typical continuous column operation, a 100 mg/L nitrate input solution was reduced to a 20 mg/L output at a feeding rate of 1500 mL/h, with a capacity of 14 kg/day/m³, and with an efficiency of 79%. In the same column, Pb(NO₃)₂ concentration was reduced from 1.0 to 0.05−0.1 mg/L and ZnSO₄ concentration was reduced from 10 to 5 mg/L.Pseudomonas aeruginosa immobilized on an O₂ plasma-treated melt blown polypropylene web was used for removing 95% of a 1.7 nCi PuCl₄ activity from a nuclear plant waste water in a batch operation.     

Detection of trace nitrite in waters using a QDs-based chemiluminescence analysis system

In the present work, a novel flow-injection chemiluminescence method based on CdTe quantum dots (QDs) was developed for the determination of nitrite. Weak chemiluminescence (CL) signals were observed from a CdTe QDs–H₂O₂ system under basic conditions. The addition of a trace amount of hemoglobin (Hb) caused the CL from the CdTe QDs–H₂O₂ system to increase substantially. In the presence of nitrite, the ferrous Hb reacted with the nitrate to form ferric Hb and NO. The NO then bound to ferrous Hb to generate iron nitrosyl Hb. As a result, the CL signal from the CdTe QDs–H₂O₂–Hb system was quenched. Thus, a flow-injection CL analytical system for the determination of trace nitrite was established. Under optimum conditions, there was a good linear relationship between CL intensity and the concentration of nitrite in the range 1.0?×?10^?9 to 8.0?×?10^?7 mol L^?1 (R ²?=?0.9957). The limit of detection for nitrite using this system was 3.0?×?10^?10 mol L^?1 (S/N?=?3). This method was successfully applied to detect nitrite in water samples.

Field determination of fluoride in drinking water using a polymeric aluminium complex of 5-(2-carboxyphenylazo)-8-hydroxyquinoline impregnated paper

A simple field method which allows the determination of fluoride in drinking water with a small handheld instrument called Arsenator was developed. Arsenator is a commercially available instrument which was used successfully for reliable determination of arsenic. In the proposed method the functionality of the Arsenator which is based on a photometric measurement of a spot on the reagent paper is expanded to analyse fluoride. A polymeric aluminium complex of 5-(2-carboxyphenylazo)-8-hydroxyquinoline (LH₂) has been prepared as a new specific reagent for fluoride. Job's method of continuous variation was adopted for the determination of the composition of the coloured complex, which was further characterized by UV-VIS spectroscopic studies. The molar absorptivity of the complex formation is 8.48?×?10³?L?mol^?1?cm^?1 at 410?nm. The coloured complex reacts with fluoride on an impregnated paper where its colour changes are dependent on the concentration of fluoride in water samples. The change in the colour was measured using the Arsenator. The method allows a reliable determination of fluoride in the range 0.3 to 2.0?mg?L^?1. Further spectophotometric determinations of fluoride in drinking water were also studied. The determination is based on the reaction of aluminium complex with fluoride in the examined samples. Beer's law is obeyed in the range 0.3 to 2.0?mg?L^?1 of fluoride at 495?nm. Sensitivity, detection limit and quantitation limit of the method were found to be 0.251?±?0.007?µg^?1?mL, 0.1?mg?L^?1 and 0.3?mg?L^?1, respectively. The optimum reaction conditions and other analytical conditions were evaluated. The effect of interfering ions on the determination is described. There is no interference by nitrate or chloride. Sulphate interfered only at high concentrations which are not expected in drinking water.     

Study of Cadmium Extraction with Aliquat 336 from Highly Saline Solutions

A large number of model solutions with high ionic strength were synthesised to mimic industrial conditions and were used as a first approach to study Cd extraction in the presence of chloride at high salinity, as experienced in real industrial solutions. The extractant used throughout in this work was Aliquat 336, a quaternary ammonium salt well known to the hydrometallurgical industry. The effects of some selected anions in addition to chloride (i.e., perchlorate, nitrate, and sulfate) were studied. The distribution of cadmium was measured using ¹⁰⁹Cd as a tracer. Liquid-scintillation spectroscopy quantified the concentration of ¹⁰⁹Cd in both phases. Raman and NMR spectroscopy were employed to gain further insight into the extraction chemistry. A careful analysis of all Cd extraction data showed that within specific windows of the reactant concentrations the chemical reactions could be represented by simplified equations, as discussed thoroughly in the text. Equilibrium constants for the extraction of \({\text{CdCl}}_{3}^{ - }\) from chloride and chloride/sulfate media were determined to be log₁₀K_ext?=?4.9?±?0.8 and log₁₀K_ext?=?5.7?±?0.5, respectively. For the nitrate environment, an exchange reaction involving a LiNO₃ ion pair is proposed and agrees with the experimental data, but was not proven. ¹⁴N-NMR and Raman spectroscopy confirmed that the relative affinity of Aliquat 336 for the relevant anions followed the order: perchlorate?>?nitrate?>?chloride?>?sulfate. Finally, ¹⁴N-NMR enabled the equilibrium constant of the exchange reaction between nitrate and chloride for Aliquat 336 to be determined.     

Kinetics of the gas-phase reactions of OH radicals with alkyl nitrates at 299 ± 2 K

Relative rate constants for the gas-phase reactions of OH radicals with a series of alkyl nitrates have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10^?12 cm³/molec·s, the rate constants obtained are (× 10¹² cm³/molec·s): 2-propyl nitrate, 0.18 ± 0.05; 1-butyl nitrate, 1.42 ± 0.11; 2-butyl nitrate, 0.69 ± 0.10; 2-pentyl nitrate, 1.87 ± 0.12; 3-pentyl nitrate, 1.13 ± 0.20; 2-hexyl nitrate, 3.19 ± 0.16; 3-hexyl nitrate, 2.72 ± 0.22; 3-heptyl nitrate, 3.72 ± 0.43; and 3-octyl nitrate, 3.91 ± 0.80. These rate constants, which are the first reported for the alkyl nitrates, are significantly lower than those for the parent alkanes, and a formula, based on the numbers of the various types of C? H bonds in the alkyl nitrates, is derived for rate constant estimation purposes.     

Photo-induced flow-injection determination of nitrate in water

A sensitive flow-injection method for the chemiluminescent determination of ultra-low concentration of nitrate in water is presented. Nitrate is on-line photolytically converted to peroxynitrite by absorption of UV light inside of 60 mm long quartz capillary (i.d. 530 µm, o.d. 720 µm). Peroxynitrite is subsequently determined by the chemiluminescent reaction with luminol. The detection limit of nitrate is 7 × 10^?10 M (S/N = 3). The linear range of the method is 2 × 10^?9–1 × 10^?5 M nitrate. The interference of nitrite is eliminated by its conversion to nitrogen after mixing of sample with a solution of sulfamidic acid. Other common anions do not interfere. The interference of cations is eliminated by passing the sample through a cation-exchange column. The FIA procedure allows analysing of 15 samples per hour. The method was applied to the determination of nitrate in various real water samples. The results are in good agreement with a reference ion chromatographic method.     

HPLC Analysis and Pharmacokinetic Study of Paeoniflorin after Intravenous Administration of a New Frozen Dry Powder Formulation in Rats

A simple and specific high performance liquid chromatographic (HPLC) method with UV detection using picroside II as the internal standard was developed and validated to determine the concentration of paeoniflorin in rat plasma and study its pharmacokinetics after an single intravenous administration of 40 mg kg^?1 paeoniflorin to Wistar rats. The analytes of interest were extracted from rat plasma samples by ethyl acetate after acidification with 0.05 mol L^?1 NaH₂PO₄ solution (pH 5.0). Chromatographic separation was achieved on an Agilent XDB C₁₈ column (250 × 4.6 mm I.D., 5 μm) with a Shim-pack GVP-ODS C₁₈ guard column (10 × 4.6 mm I.D., 5 μm) using a mobile phase consisting of acetonitrile–water–acetic acid (18:82:0.4, v/v/v) at a flow rate of 1.0 mL min^?1. The UV detection was performed at a wavelength of 230 nm. The linear calibration curves were obtained in the concentration range of 0.05–200.0 μg mL^?1 in rat plasma with the lower limit of quantification (LLOQ) of 0.05 μg mL^?1. The intra- and inter-day precisions in terms of % relative standard deviation (RSD) were lower than 5.7 and 8.2% in rat plasma, respectively. The accuracy in terms of % relative error (RE) ranged from ?1.9 to 2.6% in rat plasma. The extraction recoveries of paeoniflorin and picroside II were calculated to be 69.7 and 56.9%, respectively. This validated method was successfully applied to the pharmacokinetic study of a new paeoniflorin frozen dry power formulation. After single intravenous administration, the main pharmacokinetic parameters t _1/2, AUC_0-∞, CL_TOT, V _Z, MRT_0-∞ and V _ss were 0.739 ± 0.232 h, 43.75 ± 6.90 μg h mL^?1, 15.50 ± 2.46 L kg^?1 h^?1, 1.003 ± 0.401 L kg^?1, 0.480 ± 0.055 h and 0.444 ± 0.060 L kg^?1, respectively.     

A Cobalt Film Electrode for Nitrite Determination in Natural Water

In this study a cobalt film electrodeposited on a copper disk (Ø=3.1 mm) was tested as electrode to measure nitrite ions in raw water. This electrode was able to determine the nitrite ions concentration in nondeaerated synthetic media and in natural water. The electrode reached a detection limit of 0.2 μmol L^?1 and has a linear concentration range of 0.4 to 2 μmol L^?1 NO₂^?. The influence of several ions such as NO₃^?, Cl^?, SO₄^2?, Mg²⁺, HCO₃^? and NH₄⁺ was also tested. The electrode was used to determine the concentration of nitrite ions in a real sample.     

Counterion binding to cationic polyelectrolytes in aqueous solution

The mean ion activity coefficient, (γ_±)_px/(γ_±)_salt for different high-linear charge density cationic polyelectrolyte fluoride, bromide, chloride and nitrate has been determined. The order found is: F^? > CI^? ≧ Br^? > NO. The results obtained with added nitrate were compared with those predicted by Iwasa, Guéron, and Weisbuch and Manning's models. The latter presents the best agreement for polyion chloride and bromide. It was possible to establish the most probable microconfiguration for the polyions studied here. Manning's theory gives a moderate agreement for polyion fluoride values compatible with a lower charge density than for polyelectrolyte chloride and bromide.     

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 Nitrite in Aqueous Solutions using the Linear Sweep Voltammetry Technique

ABSTRACT

An electrochemical method using linear sweep voltammetry techniques was developed to determine nitrite ion in aqueous solution in the presence of nitrate. Nitrite solutions exhibited a well-defined oxidation wave at +1.0V vs SCE at vitreous carbon, while no oxidation process was observed for nitrate solutions. The pH of the nitrite solutions varied from 2.37 to 5.60 and no change was observed in the Ep values, except for the pH 5.60 solution, where little change was verified. The potential also did not vary with change in the nitrite concentration in the 5.0 x 10^?5 to 7.0 x 10^?4 mol L^?1 range. Very good straight lines for plots of current versus nitrite concentration in the 7.0 x 10^?5 to 7.0 x 10^?4 mol L^?1 range were obtained; the correlation coefficient was never worse than 0.990. The nitrite determination was also performed in the presence of 1.0 x 10^?3 mol L^?1 of NO₃ ^? ions. The addition of NO₃ ^? did not change significantly the current values even when it was added in one hundred times molar excess.     

Determination of Chloride 3-Methyl-9-(2-oxa-2λ5-2H-1,3,2-oxazaphosphorine-2-cyclohexyl)-3,6,9-triazaspiro [5.5] undecane (SLXM-2) in Rats by LC: Application to a Pharmacokinetic Study

A novel and simple liquid chromatographic (LC) method was developed for quantification of a new anticancer compound, chloride 3-methyl-9-(2-oxa-2λ5-2H-1,3,2-oxazaphosphorine-2-cyclohexyl)-3,6,9-triazaspiro [5.5] undecane (SLXM-2) in rat plasma. The present method used protein precipitation for extraction of SLXM-2 from rat plasma. Separation was carried out on a reversed-phase C₁₈ column (150 mm × 4.6 mm i.d., 5 μm). The mobile phases consisted of acetonitrile and 2 mM sodium dodecyl sulfate (SDS) (24:76, v/v). The flow rate was 1.0 mL min^?1. A diode-array detector (DAD) was used and the column effluent was monitored at 192 nm. Regression equations revealed good linear relationship between the peak area and the concentration. The correlation coefficient was 0.9996. The relative standard deviations (RSD) of the precision and accuracy were <9.0% (intra-day) and <6.1% (inter-day), respectively. The recovery and stability were found satisfactory during the study. The method was successfully applied for the pharmacokinetic study of SLXM-2 in rats. After a single dose (400 mg kg^?1) of SLXM-2 was given to rats by intravenous injection, the half-life of SLXM-2 was 0.304 h, the area under the plasma concentration–time curve was 673.1 μg h mL^?1 and the maximal plasma concentration was 1534.9 ± 185.8 μg mL^?1.     

Spectrophotometric Determination of Nitrite in Water Samples with 4‐(1‐Methyl‐1‐Mesitylcyclobutane‐3‐yl)‐2‐Aminothiazole

Abstract

A simple, sensitive, and specific spectrophotometric method for the measurement of nitrite in water has been developed and optimum reaction conditions along with other analytical parameters have been evaluated. The azo dye, 4‐(1‐methyl‐1‐mesitylcylobutane‐3‐yl)‐2‐(p‐N,N‐dimethylazobenzene)‐1,3‐thiazole was synthesized with the reaction of 4‐(1‐methyl‐1‐mesitylcylobutane‐3‐yl)‐2‐aminothiazole and N,N‐dimethyl aniline in acidic medium. Obtained azo dye has been characterized by infrared (IR), ¹H nuclear magnetic resonance (NMR), and microanalysis methods. The dye shows an absorption maximum at 482 nm. The method is optimized for acid concentration, pH, amount of reagents required, time, and interfering species. All the determinations were carried out at this wavelength throughout the work. At an analytical wavelength of 482 nm, Beer's law is obeyed over the concentration range 0.05 to 2.00 µg nitrite per mL analyte. The molar absorptivity, Sandell's sensitivity, and relative standard deviation are 2.03×10⁴ L mol^?1 cm^?1±251.3 (95%), 2.28×10^?3 µg cm^?2, and 2.74% (n=10), respectively. The detection limit of the method is 0.012 µg ml^?1 of nitrite ion. The method was succesfully applied to the determination of nitrite in tap water and lake water.