Simultaneous determination of nitrite and nitrate in potato and water samples using negative electrospray ionization ion mobility spectrometry

Nowadays, nitrite and nitrate ions are analyzed in biological samples using laborious and expensive methods; such as HPLC, CE, MS-MS. In this work, the simultaneous analysis of nitrite and nitrate ions was conducted by electrospray ionization-ion mobility spectrometry (ESI-IMS), without using any complicated or laborious derivitization step. Ion mobility spectrometry with low cost, inexpensive maintenance and very fast analysis makes an attractive technique for the simultaneous determination of these ions in foodstuff and drinking water samples. The analyte interference was systematically investigated for binary mixture analysis. The obtained results provided detection limits of 3.8 and 4.7 μg/L for nitrite and nitrate, respectively. A linear dynamic range of about 2 orders of magnitude, and relative standard deviations below 5% were obtained by the proposed method for the analysis of both ions. Also, the proposed method was used to analyze various real samples of potato and drinking water samples, and the obtained results confirmed the capability of negative ESI-IMS for the simultaneous detection of nitrite and nitrate.     

Simultaneous determination of inorganic and organic gunshot residues by capillary electrophoresis

A capillary electrophoresis method was developed to analyze simultaneously 11 organic and 10 inorganic components of gunshot residues as a cheaper and possibly more specific method comparing to traditional techniques. Pre-capillary complexation and simultaneously a micellar phase were combined to determine not only the metal but also the organic residues from a firearm. In order to test the possibility to apply the developed method to real cases, residues from shot samples from different firearms were analyzed and their results were compared with those obtained with electrothermal atomic absorption spectroscopy, an established technique for gunshot residue analysis. Good agreement between both techniques for lead was found.     

Chemometric approach to the optimisation of LC-FL and GC-MS methods for the determination of nitrite and nitrate in some biological,food and environmental samples

Gas chromatography–mass spectrometry (GC-MS) method and a liquid chromatography–fluorescence (LC-FL) detection method using experimental design and optimisation approach were improved for the quantitative determination of nitrite and nitrate in biological, food and environmental samples. The obtained recoveries of nitrite and nitrate ions from samples based on both GC-MS and LC-FL results ranged from 98.5% to 98.9% for nitrite and 97.9% to 98.4% for nitrate. The precision of these methods, as indicated by the relative standard deviations (RSDs), was within the range from 2.4% to 3.6% for nitrite and 2.5% to 3.8% for nitrate, respectively. The limits of detection of nitrite and nitrate ions from samples based on GC-MS and LC-FL results ranged from 0.01 to 0.14 ng L^?1 for nitrite and 0.02 to 0.71 ng L^?1 for nitrate, respectively. The optimised isolation procedure by central composite design was successfully applied to real samples. The results revealed that the proposed procedure combined with GC-MS and LC-FL techniques is more sensitive, reliable and selective compared to the other methods available for the precise determination of trace levels of nitrite and nitrate in biological, food and environmental samples.     

Flow-injection analysis of nitrate by reduction to nitrite and gas-phase molecular absorption spectrometry

Two flow-injection manifolds have been investigated for the determination of nitrate. These manifolds are based on the reduction of nitrate to nitrite and determination of nitrite by gas-phase molecular absorption spectrophotometry. Nitrate sample solution (300 microL) which is injected to the flow line, is reduced to nitrite by reaction with hydrazine or passage through the on-line copperized cadmium (Cd-Cu) reduction column. The nitrite produced reacts with a stream of hydrochloric acid and the evolved gases are purged into the stream of O2 carrier gas. The gaseous phase is separated from the liquid phase using a gas-liquid separator and then swept into a flow-through cell which has been positioned in the cell compartment of an UV-visible spectrophotometer. The absorbance of the gaseous phase is measured at 204.7 nm. A linear relationship was obtained between the intensity of absorption signals and concentration of nitrate when Cd-Cu reduction method was used, but a logarithmic relationship was obtained when the hydrazine reduction method was used. By use of the Cd-Cu reduction method, up to 330 microg of nitrate was determined. The limit of detection was 2.97 microg nitrate and the relative standard deviations for the determination of 12.0, 30.0 and 150 microg nitrate were 3.32, 3.87 and 3.6%, respectively. Maximum sampling rate was approximately 30 samples per hour. The Cd-Cu reduction method was applied to the determination of nitrate and the simultaneous determination of nitrate and nitrite in meat products, vegetables, urine, and a water sample.     

Simultaneous determination of bromide, nitrite and nitrate ions in seawater by capillary zone electrophoresis using artificial seawater as the carrier solution

We describe capillary zone electrophoresis (CZE) for the simultaneous determination of bromide, nitrite and nitrate ions in seawater. Artificial seawater was adopted as the carrier solution to eliminate the interference of high concentrations of salts in seawater. The artificial seawater was free from bromide ion to enable the determination of bromide ion in a sample solution. For the purpose of reversing the electroosmotic flow (EOF), 3 mM cetyltrimethylammonium chloride (CTAC) was added to the carrier solution. A 100 microm ID (inside diameter) capillary was used to extend the optical path length. The limits of detection (LODs) for bromide, nitrite, and nitrate ions were 0.46, 0.072, and 0.042 mg/L (as nitrogen), respectively. The LODs were obtained at a signal to noise ratio (S/N) of 3. The values of the relative standard deviation (RSD) of peak area for these ions were 1.1, 1.5, and 0.97%. The RSDs of migration time for these ions were 0.61, 0.69, and 0.66%. Artificial seawater samples containing various concentrations of bromide, nitrite, and nitrate ions were analyzed by the method. The error was less than +/-12% even if the concentration ratio of bromide ion to nitrite or nitrate ion was 20-240. The proposed method was applied to the determination of bromide, nitrite, and nitrate ions in seawater samples taken from the surface and the seabed. These ions in other environmental waters such as river water and rainwater samples were also determined by ion chromatography (IC) as well as this method.     

毛细管离子电泳法同时测定腌菜中硝酸根和亚硝酸根

以溴离子(Br-)为内标,建立了毛细管离子电泳同时测定腌菜中的硝酸根和亚硝酸根的方法。讨论了缓冲液pH、样品和缓冲液中氯化钠浓度、分离电压对分离的影响。结果表明:以含1mol LNaCl的40mmol LH3PO4 NaOH缓冲-、-得到基线分离。NO3-和NO2液(pH3.5)为背景电解质,4min内Br-、NO3-检出限分别为0.1g L和0.3g L,峰面积相对标准偏差分别为4.6%和NO25 8%。     

Two-dimensional nano-liquid chromatography-mass spectrometry system for applications in proteomics

Transient isotachophoresis-capillary zone electrophoresis with artificial seawater as the background electrolyte (BGE) was improved to further lower the limit of detection (LOD) for determination of nitrite and nitrate in seawater. By lowering the pH of BGE, the difference between effective mobility of nitrite and that of nitrate increased, thereby permitting increased sample volumes to be tolerated and their LOD values to decrease. Artificial seawater with pH adjusted to 3.0 using phosphate buffer was adopted as the BGE. To reverse electroosmotic flow (EOF), a capillary was flushed with 0.1 mM dilauryldimethylammonium bromide for 3 min before the capillary was filled with the BGE. Limits of detection (LODs) for nitrite and nitrate were 2.7 and 3.0 microg/l (as nitrogen), respectively. The LODs were obtained at a signal-to-noise ratio of 3. Values of the relative standard deviation (RSD) of peak area for these ions were 2.0 and 0.75%, respectively, when nitrite concentration was 0.05 mg/l and that of nitrate was 0.5 mg/l. The RSDs of peak height were 4.4 and 2.3%. The RSD values of migration time for these ions were 0.19 and 0.17%. The proposed method was applied to determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater, MOOS-1, distributed by the National Research Council of Canada. Results agreed with the assigned tolerance interval. This method was also applied to determination of these ions in seawater collected around Osaka Bay. Results nearly agreed with those obtained by a conventional spectrophotometric method.     

On-line ion-exchange preconcentration in a flow injection system coupled to capillary electrophoresis for the direct determination of UV absorbing anions

On-line ion-exchange preconcentration, performed in a flow injection analysis system, has been integrated with capillary electrophoresis via a specially designed interface, and a sensitive and selective method for the determination of nitrite, nitrate, bromide and iodide using direct UV absorbance detection has been developed. Fivefold enrichment of these aforementioned anions can be realised. Separation conditions such as carrier electrolyte and concentration of electroosmotic modifier were investigated. Limits of detection were ca. 10 ng ml⁻¹ for nitrite and nitrate in aqueous samples, and the overall relative standard deviation was about 5%.     

High-throughput nitric oxide assay in biological fluids using microchip capillary electrophoresis

In order to develop a high-throughput screening method for the nitrogen monoxide metabolites, nitrite and nitrate, in biological fluids, we have investigated the simultaneous determination of these metabolites using microchip capillary electrophoresis (MCE). In this study, the control of applied voltage to obtain higher sensitivity by increasing the sample injection volume was investigated. Also, the improvement of reproducibility by correcting the injection volume using the internal standard was investigated. By increasing the sample volume, the limits of detection achieved for nitrite and nitrate were 24 and 12 microM, respectively. Because we used a 10-fold diluted sample when detecting nitrite and nitrate in human serum, it was necessary to increase the sensitivity by a factor of 10-50. The run-to-run and day-to-day relative standard deviations achieved were improved to less than 10% by using an internal standard to correct the injection volume. Moreover, we obtained successful separation of nitrite and nitrate in spiked human serum within 6.5 s under optimum analytical conditions. As a result, although it is necessary to obtain greater sensitivity, it was concluded that determination of the amount of NO metabolites in biological fluids using MCE is possible.     

Optimum conditions for effective use of the terminating ion in transient isotachophoresis for capillary zone electrophoretic determination of nitrite and nitrate in seawater,with artificial seawater as background electrolyte

We have examined transient isotachophoresis (ITP) conditions, e.g. the nature of the terminating ion, its concentration, and the injection procedure, to improve the limit of detection (LOD) for determination of nitrite and nitrate in seawater by capillary zone electrophoresis (CZE). Artificial seawater containing 3.0 mmol L(-1) cetyltrimethylammonium chloride (CTAC) was used as background electrolyte (BGE). After sample injection 600 mmol L(-1) acetate was separately injected into the capillary as the terminating ion for transient ITP. The LOD for nitrite and nitrate, obtained at a signal-to-noise ratio (S/N) of 3, were 15 and 7.0 microg L(-1) (as nitrogen), respectively. Relative standard deviations (RSD) of peak area for nitrite and nitrate were 7.3 and 0.8%, respectively, and the RSD of peak height were 5.7 and 1.2%, respectively, when the concentrations of nitrite and nitrate were 0.05 and 0.25 mg L(-1). The RSD of migration time for these ions was 0.2%. The proposed method was applied to the determination of nitrite and nitrate in seawater samples. The results for nitrite were nearly in agreement with those obtained by naphthylethylenediamine spectrophotometric analysis (SPA; correlation coefficient 0.9041).     

Determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater by capillary zone electrophoresis with artificial seawater as the background electrolyte using transient isotachophoresis

We describe a combination of selected ions as a terminating ion which is useful for transient isotachophoresis (ITP) in capillary zone electrophoresis (CZE) for the determination of nitrite and nitrate in seawater. In addition to 150 mM sulfate as the principal terminating ion, 10 mM bromate was added to a sample solution as the additional terminating ion. Artificial seawater containing 3 mM cetyltrimethylammonium chloride (CTAC) was adopted as a background electrolyte (BGE). The limits of detection (LODs) for nitrite and nitrate were 2.2 and 1.0 microg/L (as nitrogen), respectively. The LODs were obtained at a signal to noise ratio (S/N) of 3. The values of the relative standard deviation (RSD) of peak area for these ions were 1.9 and 1.4%. The RSDs of peak height were 1.7 and 1.9%, the RSDs of migration time 0.11%. The proposed method was applied to the determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater, MOOS-1, distributed by the National Research Council of Canada (NRC). The results almost agreed with the assigned tolerance interval.     

Simultaneous determination of the three main inorganic forms of nitrogen by ion chromatography

An ion chromatographic method for the determination of nitrite, nitrate and ammonium simultaneously is described. An appropriate eluent-column-detector combination for separating and detecting these ions is discussed. On a bifunctional ion-exchange column, nitrite and nitrate anions were separated by anion exchange and ammonium cation by cation exchange. Nitrite and nitrate were detected by UV spectrometry and ammonium using a chemically suppressed conductivity detector. The detection limits for the three ions were all below 0.02 ppm (w/w) and the relative standard deviations for the three ions were all less than 0.5%. Several samples such as water, soil and acid rain were analysed with this method and the recoveries of the three ions were all within 100 ± 5%. These results agreed well with those obtained by a standard method.     

Development of a simple method for the determination of nitrite and nitrate in groundwater by high-resolution continuum source electrothermal molecular absorption spectrometry

In this work, it was developed a method for the determination of nitrite and nitrate in groundwater by high-resolution continuum source electrothermal molecular absorption spectrometry of NO produced by thermal decomposition of nitrate in a graphite furnace. The NO line at 215.360 nm was used for all analytical measurements and the signal obtained by integrated absorbance of three pixels. A volume of 20 μL of standard solution or groundwater sample was injected into graphite furnace and 5 μL of a 1% (m/v) Ca solution was co-injected as chemical modifier. The pyrolisis and vaporization temperatures established were of 150 and 1300 °C, respectively. Under these conditions, it was observed a difference of thermal stability among the two nitrogen species in the presence of hydrochloric acid co-injected. While that the nitrite signal was totally suppressed, nitrate signal remained nearly stable. This way, nitrogen can be quantified only as nitrate. The addition of hydrogen peroxide provided the oxidation of nitrite to nitrate, which allowed the total quantification of the species and nitrite obtained by difference. A volume of 5 μL of 0.3% (v/v) hydrochloric acid was co-injected for the elimination of nitrite, whereas that hydrogen peroxide in the concentration of 0.75% (v/v) was added to samples or standards for the oxidation of nitrite to nitrate. Analytical curve was established using standard solution of nitrate. The method described has limits of detection and quantification of 0.10 and 0.33 μg mL⁻¹ of nitrogen, respectively. The precision, estimated as relative standard deviation (RSD), was of 7.5 and 3.8% (n = 10) for groundwater samples containing nitrate–N concentrations of 1.9 and 15.2 μg mL⁻¹, respectively. The proposed method was applied to the analysis of 10 groundwater samples and the results were compared with those obtained by ion chromatography method. In all samples analyzed, the concentration of nitrite–N was always below of the limit of quantification of both the methods. The concentrations of nitrate–N varied from 0.58 to 15.5 μg mL⁻¹. No significant difference it was observed between the results obtained by both methods for nitrate–N, at the 95% confidence level.     

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.     

Spectroscopic determination of sulphate in the presence of excess of nitrate and nitrite

The KBr pellet technique has been used for the determination of alkali metal sulphate in the presence of large excesses of nitrate and nitrite by measuring the absorption of the sulphate at 619 cm(-1). The sulphate can be determined in a 400-fold molar excess of nitrate and a 60-fold molar excess of nitrite with a relative standard deviation of about 5%.     

Use of Griess reagent containing vanadium(III) for post-column derivatization and simultaneous determination of nitrite and nitrate in baby food

An ion chromatographic method with post-column derivatization and spectrophotometric detection is presented for the determination of nitrate and nitrite (NOx) in baby food. NOx residues found naturally or added as preservatives were extracted from baby foods and determined by using ion chromatography with post-column derivatization and spectrophotometric detection. Nitrate was reduced to nitrite online by post-column reduction using vanadium(lll) chloride and heat. Nitrite reacted with Griess reagent to produce a dye that was detected at 525 nm. The use of V(III) and heat to promote the reduction of nitrate to nitrite online is a novel feature of this detection system. The determination of incurred NOx residues in samples by using AOAC Method 993.03 yielded results comparable to those obtained by ion chromatography with spectrophotometric detection. The toxic and carcinogenic metal cadmium used in the AOAC Method to reduce the nitrate to nitrite was avoided. The proposed method provides simultaneous determination of nitrate and nitrite. Average recoveries of nitrate and nitrite residues ranged from 82 to 107% for fortification levels of 25-400 ppm.     

Application of manganese(IV) dioxide microcolumn for determination and speciation of nitrite and nitrate using a flow injection analysis-flame atomic absorption spectrometry system

A flow injection (FI) method with flame atomic absorption spectrometry (FAAS) detection was developed for the determination and speciation of nitrite and nitrate in foodstuffs and wastewaters. The method is based on the oxidation of nitrite to nitrate using a manganese(IV) dioxide oxidant microcolumn where the flow of the sample through the microcolumn reduces the MnO₂ solid phase reagent to Mn(II), which is measured by FAAS. The absorbance of Mn(II) are proportional to the concentration of nitrite in the samples. The injected sample volume was 400 μL with a sampling rate of analyses was 90 h⁻¹ with a relative standard deviation better than 1.0% in a repeatability study. Nitrate is reduced to nitrite in proposed FI-FAAS system using a copperized cadmium microcolumn and analyzed as nitrite. The calibration curves were linear up to 20 mg L⁻¹ and 30 mg L⁻¹ with a detection limit of 0.07 mg L⁻¹ and 0.14 mg L⁻¹ for nitrite and nitrate, respectively. The results exhibit no interference from the presence of large amounts of ions. The method was successfully applied to the speciation of nitrite and nitrate in spiked natural water, wastewater and foodstuff samples. The precision and accuracy of the proposed method were comparable to those of the reference spectrophotometric method.     

Flow injection catalytic spectrophotometric simultaneous determination of nitrite and nitrate

A new flow injection catalytic spectrophotometric method is proposed for the simultaneous determination of nitrite and nitrate based on the catalytic effect of nitrite on the redox reaction between crystal violet and potassium bromate in phosphoric acid medium and nitrate being on-line reduced to nitrite with a cadmium-coated zinc reduction column. The redox reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of crystal violet at the maximum absorption wavelength of 610 nm. A technique of inserting a reduction column into sampling loop is adopted and the flow injection system produces a signal with a shoulder. The height of shoulder in the ascending part of the peak corresponds to the nitrite concentration and the maximum of the peak corresponds to nitrate plus nitrite. The detection limits are 0.3 ng ml⁻¹ for nitrite and 1.0 ng ml⁻¹ for the nitrate. Up to 32 samples can be analyzed per hour with a relative standard deviation of less than 2%. The method has been successfully applied for the simultaneous determination of nitrite and nitrate in natural waters.     

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.     

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.