Sensitive Determination Of Nitrite Research Articles

Magnetic Three-Dimensional Graphene: A Superior Adsorbent for Selective and Sensitive Determination of Nitrite in Water Samples by Ion-Pair Based-Surfactant-Assisted Solid-Phase Extraction Combined with Spectrophotometry

A straightforward, fast and efficient analytical method was developed which utilizes a magnetic composite called three-dimensional graphene (3D-G@Fe3O4) as an adsorbent to recover nitrite ions (NO2−) from environmental water samples. The investigation into the synthesized adsorbent contained an examination of its morphology, chemical composition, structural attributes, and magnetic properties. This comprehensive analysis was conducted using various instrumental techniques, including Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), and vibrating sample magnetometry (VSM). The adsorbent surface was activated by adding cetyltrimethylammonium bromide (CTAB) to the sample solution. To improve the selectivity and sensitivity of the method, nitrite ions were reacted with sulfanilic acid and chromotropic acid sequentially. An orange-red azo-dye complex was formed in the presence of nitrite ions with a clear absorbance peak at 514 nm. The effect of the main experimental parameters such as the pH of the sample solution, adsorbent dosage, and CTAB dosage was explored, and the optimization process was performed using a central composite design (CCD). The linear dynamic range (20–100 ng mL−1) was determined under optimal experimental circumstances, yielding a reasonable determination coefficient (R2, 0.9993), a detection limit of 5.12 ng mL−1, an enrichment factor of 167, and precision values of 1.0% intraday and 2.9% inter-day. The methodology successfully identified minute nitrite ions in environmental water samples with relative recoveries that varied between 96.05 and 101.6 ng mL−1.

Parts per billion of nitrite in microcrystalline cellulose by ion chromatography mass spectrometry with isotope labeled internal standard

Regulatory authorities like the U.S. Food and Drug Administration (FDA) have set strict specification levels for N-nitrosamines in finished drug products. Nitrite is a potential precursor for the formation of probable carcinogenic N-nitrosamines when secondary or tertiary amines are also present in the active pharmaceutical ingredient (API) synthesis or drug formulation process. An accurate and sensitive determination of nitrite will be useful when a drug product manufacturer chooses to investigate the reaction kinetics between nitrite and amines or to select appropriate excipients for its drug formulation. Pharmaceutical excipient manufacturers may also need an accurate nitrite measurement to investigate the nitrite content in their excipients. This study details the development and validation of an ion chromatography mass spectrometry (IC-MS) method for trace nitrite determination in microcrystalline cellulose materials, one of the important pharmaceutical excipients used in many drug formulations. MS operated under selected ion monitoring mode was used to solve the commonly encountered interference issue with conductivity detection, and nitrite isotope internal standard was employed to address the ion suppression issue with MS detection. The installation of an after-column “jumper” to flush water with an auxiliary pump through the MS when it is not used for data collection avoided sensitivity loss due to trace salt accumulation in the ion source. Validation of the optimized method was satisfactory, with linearity of nitrite in the concentration range of 0.02–7.50 ppm (µg/g) having a regression coefficient of > 0.999, precision of RSD < 9.5% at 0.03 ppm and RSD < 3.4% at 0.4 ppm and recovery of 92.0–103.0%. The limit of detection and limit of quantitation were 0.005 and 0.016 ppm, respectively.

Plasmon-Mediated Oxidase-like Activity on Ag@ZnS Heterostructured Hollow Nanowires for Rapid Visual Detection of Nitrite.

Rational design of fast and sensitive determination of nitrite (NO2-) from a complicated actual sample overtakes a crucial role in constructing a high-efficiency sensing platform. Herein, a visual NO2- sensing platform with outstanding selectivity, sensitivity, and stability based on a surface plasmon resonance (SPR)-enhanced oxidase-like activity has been proposed. Benefiting from the intrinsic photocatalytic activity and limited light penetration of ZnS, the oxidase-like activity based on ZnS decorated on Ag nanowires (Ag@ZnS) is determined. It is demonstrated that the electrons are generated efficiently on the surface of ZnS and then transferred into the hot electrons of Ag with the help of localized SPR excitation, thus greatly oxidating the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to produce dark blue oxidized TMB (oxTMB). When nitrite is added into the reaction system, the oxTMB will selectively react with NO2- to generate diazotized oxTMB, leading to a visual color change from dark blue to light green and subsequently to dark yellow. Owing to the specific recognition between nitrite and oxTMB, the recovery of catalytic activity induced an enhanced colorimetric test with a wider linear range for NO2- determination, an ultralow detection limit of 0.1 μM, excellent selectivity, and practicability for application in real samples. This plasmon-enhanced oxidase-like activity not only provides a smart approach to realize a colorimetric assay with high sensitivity and simplicity but also modulates oxidase-like activities.

Selective determination of nitrite in water and food samples using zirconium oxide (ZrO2)@MWCNTs modified screen printed electrode.

Nitrite ions are being used in different forms as food preservatives acting as flavor enhancers or coloring agents for food products. However, continuous ingestion of nitrite may have severe health implications due to its mutagenic and carcinogenic effects. Thus, this study constructed an electrochemical assay using disposable nano-sensor chip ZrO2@MWCNTs screen printed electrodes (SPE) for the rapid, selective, and sensitive determination of nitrite in food and water samples. As a sensing platform, the use of nanomaterials, including metal oxide nanostructures and carbon nanotubes, exhibited a superior electrocatalytic activity and conductivity. Morphological, structural, and electrochemical analyses were performed using electron microscopy (SEM and TEM), Fourier-transform infrared (FTIR) spectroscopy, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronoamperometry (CA). Accordingly, a wide dynamic linear range (5.0 μM to 100 μM) was obtained with a limit of detection of 0.94 μM by the chronoamperometric technique. In addition, the sensor's selectivity was tested when several non-target species were exposed to the sensor chips while no obvious electrochemical signals were generated when the nitrite ions were not present. Eventually, real food and water sample analysis was conducted, and a high recovery was achieved.

Elaeocarpus Ganitrus Structured Mesoporous Hybrid Mn3+/4+ loaded Zirconia Self Assembly as a Versatile Amperometric Probe for the Electrochemical Detection of Nitrite

AbstractSelective and highly sensitive detection of nitrite is always a challenge for electrochemist for the administration of nitrite in water and food samples. In this regard nanostructured materials are crown choice. In the present investigation, we have prepared uniformly ordered hybrid Mn3+/4+ : ZrO2 nanoganitrus via hydrothermal method, characterized by XRD, BET, SEM, TEM and XPS to understand the structural and morphological features of the material and used for the electrocatalytic determination of nitrite. The preparation process resulted in the formation of nanoganitrus heterostructures with honeycomb arrangement. High surface area, ganitrus structure and hybrid Mn3+/4+ in the material was correlated to its robust electrochemical performance. Thus, prepared sensor showed highly selective and sensitive determination of nitrite with a good linear range of 250 μM to 10,000 μM with correlation coefficient of 0.998 and a sensitivity of 38.8 μAmM−1 cm−2. The limit of Detection of nitrite sensing system was 93 μM at a signal to noise ratio of 3. Also, the sensor showed prominent reproducibility, good stability, anti‐interference performance and also the prepared sensor was successfully used for the detection of nitrite in real samples.

Fabrication of Electrochemical Sensor Based on CeO2−SnO2 Nanocomposite Loaded on Pd Support for Determination of Nitrite at Trace Levels

AbstractHere, an electrochemical sensor based on CeO2‐SnO2/Pd was prepared and used for highly selective and sensitive determination of nitrite in some real samples. This nanocomposite was characterized by various methods like X‐ray photoelectron spectroscopy, X‐ray diffraction, energy dispersive spectroscopy, Fourier‐transform infrared spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The electrochemical behavior of the sensor was evaluated by cyclic voltammetry. The results showed excellent catalytic property of the nanocomposite as a an electrocatalyst for nitrite oxidation. In the following, the experimental parameters affecting the analytical signal for nitrite were optimized. Under the optimal conditions, the limit of detection and sensitivity of the sensor were calculated as 0.10 μM and 652.95 μA.mM−1.cm−2, respectively. Also, the response of the sensor was linear in the range of 0.36 to 2200 μM of nitrite. Finally, some of the inherent features of the sensor such as repeatability, reproducibility and stability were examined after evaluation of the sensor selectivity in the presence of several interfering species.

Redox-derivatization reaction-based rapid and sensitive determination of nitrite using resonance Rayleigh scattering method.

It remains a problem for direct detection of small inorganic nitrite ions using resonance Rayleigh scattering (RRS) method based on the direct dye-binding reaction. In the present study, a redox-derivatization reaction taking only 5min was introduced prior to nitrite detection. In the redox-derivatization reaction, nitrite ions were reduced by excess iodine ions to generate triiodide ions (I3-), which were further derivatized with a cationic dye (basic violet 1, BV1) to form the ion associates of I3--BV1. Therefore, the RRS signal was significantly enhanced, resulting from the increase of particle size and resonance-enhanced scattering effect. The analytical procedure was performed by just mixing nitrite, oxidant, acid, and dye all-in-one, avoiding the tediousness of a multi-step process or the preparation of nanoparticles. The whole detection process including the redox-derivatization reaction was less than 6min. The reaction conditions such as concentration of hydrochloric acid, potassium iodide, and BV1, reaction time, and temperature were investigated. Under optimum conditions, the concentration of nitrite was linear with an RRS signal of I3--BV1 ion associates at 320nm in the range of 0.015-1.2mg/L. The limit of detection (LOD) was calculated to be 3.0μg/L. The RRS method was applied to the determination of nitrite in real samples such as pork sausage, milk powder, and water with recovery of 95.2-112%. With advantages of rapidness, high sensitivity, and high selectivity, the method indicates potential applicability for detection of nitrite in complex samples. The method also provides an instructive protocol for detection of analytes that generate no/weak RRS enhancement after the direct dye-binding reaction. Graphical abstract.

Sensitive determination of nitrite by using an electrode modified with hierarchical three-dimensional tungsten disulfide and reduced graphene oxide aerogel.

Nanosheets of tungsten disulfide (WS2) were used to improve the physicochemical properties of reduced graphene oxide aerogel (rGA). The nanosheets were directly integrated into 3D hybrid architecture of rGA by a solvothermal mixing method by which the WS2 sheets were assembled onto the conductive graphene network. WS2 with highly exfoliated and defect-rich structure made the WS2/rGA composite possess plentiful active sites, and this enhanced the electrocatalytic capability of the composite. The introduction of poorly conductive WS2 into 3D rGA system decreases the background current of rGA when used as electrode material. This is advantageous in terms of signal to-noise ratio and analytical performance in general. The WS2/rGA electrode, best operated at a potential of 0.68V (vs. SCE) has a linear response in the 0.01 to 130μM nitrite concentration range with a low detection limit of 3nM (at S/N = 3). It is selective, reproducible, stable and is successfully applied to the determination of nitrite in spiked bacon samples. Graphical Abstract Schematic presentation of an electrochemically modified electrode for the detection of nitrite based on 3D tungsten disulfide/reduced graphene oxide aerogel (WS2/rGA).

Nitrogen-doped-carbon-coated hexagonal cobalt oxyhydroxide/reduced graphene oxide nanocomposite for sensitive and selective detection of nitrite in human hepatoma cells

Selective and sensitive determination of nitrite is of great importance in practical application. In the present work, a novel nitrite sensing platform was built based on the fabrication of nitrogen-doped-carbon-coated hexagonal cobalt oxyhydroxide (CN@CoOOH) on reduced graphene oxide (RGO) using zeolitic imidazolate framework (ZIF)-67 as a precursor. The CN@CoOOH/RGO nanocomposite was confirmed by UV–visible spectroscopy, Fourier transform infrared spectroscopy, x-ray photoelectron spectrum, transmission electron microscopy, scanning electron microscopy, and x-ray diffraction. We applied the nanocomposite to detect nitrite selectively and sensitively through amperometry for the first time. The anodic current values increased with the addition of nitrite. Therefore, the concentrations of nitrite were quantitatively detected using a CN@CoOOH/RGO based sensor. A wider linear range of 0.1 to 7000 μM was obtained with a lower detection limit of 10 nM (S/N = 3). The proposed method was also applied to detect nitrite released from normal liver cells and human hepatoma cells.

Nonenzymatic nitrite sensor based on a titanium dioxide nanoparticles/ionic liquid composite electrode

A titanium dioxide nanoparticles/ionic liquid composite electrode was prepared and used for selective and sensitive determination of nitrite. The electrochemical behavior of the modified electrodes and the mechanism of the oxidation of nitrite were investigated using cyclic voltammetry. The effect of working solution pH, scan rate and the amount of modifier were studied in great detail. The modifier titanium dioxide nanoparticles in the carbon paste increased the effective surface area of the electrode evidently and improved the sensitivity by enhancing peak currents. Moreover, the presence of high conductive ionic liquids promoted the electron transfer rate and decreased the overpotential of the oxidation of nitrite compared with other electrodes. The proposed sensor showed electrocatalytic activity for the oxidation of nitrite and the oxidation peak occurred at low overpotential (0.78V versus Ag/AgCl). The catalytic peak current was found to be linear with the nitrite concentration in the range of 5×10−7–1.5×10−3M, with a correlation coefficient of 0.9977, using linear sweep voltammetry. The detection limit of 2×10−7M was obtained at a signal-to-noise ratio of 3. The sensor had good reproducibility and stability. The proposed method was applied for the voltammetric determination of nitrite in some sausage samples, and satisfactory results were obtained.

A nitrite and hydrogen peroxide sensor based on Hb adsorbed on Au nanorods and graphene oxide coated by polydopamine

A novel hemoglobin (Hb) electrode modified with Au nanorods (AuNRs) and graphene oxide sheets (GOs) coated by polydopamine (Pdop) (GOs@Pdop) was fabricated and used for highly selective and sensitive determination of nitrite (NO2−) and hydrogen peroxide (H2O2). The electrochemical characteristics of the sensor were studied by cyclic voltammetry and chronoamperometry. The GOs@Pdop composite was characterized by Fourier transform infrared (FTIR), ultraviolet-vis absorption spectroscopy (UV-vis) and transmission electron microscopy (TEM). The system was optimized to realize a reliable determination of NO2− at 0.7 V with a detection limit of 2.5 × 10−8 M and H2O2 at –0.2 V with a detection limit of 2.0 × 10−6 M (S/N = 3). The apparent Michaelis–Menten constants (KappM) were calculated to be 0.13 mM for NO2− and 0.70 mM for H2O2. Moreover, the sensor obtained from this study exhibited high sensitivity, good reproducibility, and long-term stability.

Surface decoration of multi-walled carbon nanotubes modified carbon paste electrode with gold nanoparticles for electro-oxidation and sensitive determination of nitrite

In this paper, a highly sensitive and selective voltammetric sensor for the determination of nitrite is proposed. We described a fast and easy method for the fabrication of gold nanoparticles/multi-walled carbon nanotube/carbon paste electrode (GNPs /MWCPE) by one-step electrodeposition under controlled potential, the whole procedure takes only several minutes. Scanning electron microscopy (SEM) image demonstrated that the gold nanoparticles deposited on MWCNTs/CPE were uniform, with an average size of 30nm. By combining the benefits of GNPs/MWCNTs and CPE, the resulted modified electrode exhibited outstanding electrocatalytic activity in terms of nitrite oxidation by giving much higher peak currents than those found for the unmodified CPE and also the MWCNTs-modified electrode. The effect of various experimental parameters on the voltammetric response of nitrite was investigated. At the optimum conditions the sensor has a linear response in the 0.05–250.0µmolL−1 concentration range, a very good detection sensitivity (0.4177μALµmol−1), and a low detection limit of 1×10−2μmolL−1 of nitrite. Most common ions and many environmental organic pollutants do not interfere. The proposed chemically modified electrode was used to the determination of NO2- in several foodstuffs and water samples and the results were found to be consistent with the values obtained by the Griess protocol.

Sensitive determination of nitrite in food samples using voltammetric techniques

A [5,10,15,20-tetrakis (4-methoxyphenyl) porphyrinato] manganese (III)chloride (TMOPPMn(III)Cl)-modified gold electrode sensor was developed for the determination of nitrite in food samples. The developed sensor showed an excellent catalytic activity and stability for nitrite oxidation. Under optimized conditions, nitrite concentration as low as 2.9 × 10−9 M can be determined in various food samples using the developed sensor. Effect of common interfering ions have been investigated in simulated mixtures containing high levels of interfering ions and the sensor was found to be tolerant against these ions. The determination of nitrite in food samples such as chicken ham, sausage and pickled vegetables with the proposed sensor was in good agreement with those obtained by standard spectrophotometric method.

Electropolymerization of Indole-3-acetic Acid on Glassy Carbon Electrode for Sensitive Detection of Nitrite

Highly uniform and adhesive films of poly(indole-3-acetic acid) (p-IAA) were fabricated on the glassy carbon electrode (GCE) by electropolymerization of indole-3-acetic acid (IAA). The p-IAA modified GCE (p-IAA/GCE) was constructed to develop a promising amperometric sensor for the sensitive determination of nitrite. Field emission scanning electron microscope (SEM) and electrochemical techniques were used for the surface characterization of the modified electrode. It was demonstrated that p-IAA modified GCE (p-IAA/GCE) exhibited remarkable electrocatalytic activity towards the oxidation of nitrite with obvious reduction of overpotential. Under the optimal conditions, the linear range for the detection of nitrite was 5.0×10-7 to 5.0×10-4 M with a high sensitivity of 0.105 AM-1, and a low detection limit of 1.0×10-7 M (S/N = 3). The influence of various anions and cations on the nitrite detection has been studied. The proposed method was successfully applied in the detection of nitrite in sausage samples, and the results were consistent with those obtained by UV-vis spectrophotometric methods.

A sensitive fluorimetric method for determination of trace amounts of nitrite based on luminescence energy transfer

Abstract An efficient luminescence energy transfer (LET) system based on terbium(III)-sodium hexametaphosphate (Tb/SHMP) chelates as donor and 4-((4-(2-aminoethylamino)naphthalen-1-yl)diazenyl)benzenesulfonic acid dihydrochloride (ANDBS) as acceptor was developed for sensitive determination of trace nitrite. Stable and strong fluorescence Tb/SHMP chelates were prepared in aqueous solution. Based on Griess Reaction, ANDBS was generated by the quantitative reaction of nitrite, sulfanilamide and N-(1-naphtyl)-ethylenediamine dihydrochloride (N1NED). The degree of the overlap was effective for LET between the emission spectrum of Tb/SHMP chelates and the absorption spectrum of ANDBS. Based on the luminescence intensity quenching of Tb/SHMP chelates in proportion to the trace amounts of nitrite, a new assay for the selective and sensitive determination of nitrite was developed. Under the optimum conditions, the linear calibration graph was obtained with a linear range of 0.00040–0.20 μg mL−1 (R=0.99657). The detection limit of NO 2 − was 0.00010 μg mL−1 (R=0.99657). The method was applied successfully to the determination of nitrite for synthetic samples.

Fabrication of DNA functionalized carbon nanotubes/Cu 2+ complex by one-step electrodeposition and its sensitive determination of nitrite

In this paper, DNA functionalized single-wall carbon nanotubes/Cu 2+ (DNA–CNTs/Cu 2+) complex was one-step electrodeposited onto the glassy carbon electrode (GCE), which fabricated a DNA–CNTs/Cu 2+/GCE sensor to detect nitrite. Cyclic voltammogram of DNA–CNTs/Cu 2+/GCE showed a pair of well-defined redox peaks for Cu 2+/Cu +. Compared with DNA–CNTs/GCE and DNA–Cu 2+/GCE, the prepared DNA–CNTs/Cu 2+/GCE exhibited more excellent electrochemical properties. Thus, the prepared DNA–CNTs/Cu 2+/GCE was proposed as nitrite sensor. The effects of Cu 2+, CNTs and DNA concentration in the mixture together with electrodeposition time and determination conditions such as applied potential, pH value on the current response of DNA–CNTs/Cu 2+/GCE toward nitrite were optimized to obtain the maximal sensitivity. In addition, electrochemical experiments revealed that the modified electrode showed high electrocatalytic activity to the reduction of nitrite ion (NO 2 −). The linear range for the detection of NO 2 − was 3 × 10 −8 to 2.6 × 10 −3 M, and the response was very fast (less than 3 s). A low detection limit of 3 × 10 −8 M (S/N = 3) for NO 2 − was achieved.

Fabrication of nano-copper/carbon nanotubes/chitosan film by one-step electrodeposition and its sensitive determination of nitrite

In this paper, Cu nanoparticles/carbon nanotube/chitosan (Cu nano/CNTs/CS) film was one-step electrodeposited onto the glassy carbon electrode (GCE), which fabricated a Cu nano/CNTs/CS/GCE sensor to detect nitrite. One-step electrodeposition of CNTs and Cu nano with the chitosan (CS) hydrogel was achieved, and the whole procedure takes only several minutes. Scanning electron microscopy (SEM) image demonstrated that the Cu nanoparticles coated on CNTs/CS were uniform, with an average size of 30 nm. The effects of Cu 2+, CNTs and CS concentration in the mixture together with electrodeposition time and determination conditions such as applied potential, pH value on the current response of Cu nano/CNTs/CS/GCE toward nitrite were optimized to obtain the maximal sensitivity. In addition, electrochemical experiments revealed that the modified electrode showed high electrocatalytic activity to the reduction of nitrite ion (NO 2 −). The linear range for the detection of NO 2 − was 1.0 × 10 −7 M to 2.5 × 10 −3 M with a high sensitivity of −48.92 μA mM −1, and the response was very fast (less than 2 s). A low detection limit of 2.4 × 10 −8 M (S/N = 3) for NO 2 − was achieved.

Electrocatalytic reduction and sensitive determination of nitrite at nano-copper coated multi-walled carbon nanotubes modified glassy carbon electrode

Abstract In this paper, Cu nanoparticles were electrodeposited onto the film of Nafion (Nf)-solubilized multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE), which fabricated a sensitive nano-copper coated multi-walled carbon nanotubes modified glassy carbon electrode (Cunano/CNTs–Nf/GCE) to detect nitrite. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) demonstrated that the Cu nanoparticles coated on MWCNTs were uniform, with an average size of 30 nm. The effects of electrodeposition circles, CNTs–Nf solution concentration and determination conditions such as pH value and applied potential on the current response of Cunano/CNTs–Nf/GCE toward nitrite were optimized to obtain the maximal sensitivity. Moreover, electrochemical experiments revealed that the modified electrode sensor showed high electrocatalytic activity for the reduction of nitrite ion ( NO 2 - ). The linear range of the determination of NO 2 - was from 1.0 × 10−6 M to 6.0 × 10−4 M and the response was fast (less than 5 s). A low detection limit of 8.0 × 10−8 M (S/N = 3) for NO 2 - was achieved.

Precise and sensitive determination of nitrite by coulometric backtitration under flow conditions

A novel method performing for coulometric backtitrations in flow channels was developed, which was applied for the precise and sensitive determination of low concentrations of nitrite. Under acid conditions nitrite is reacting stoichiometrically with hydrazine, the remained excess of which is backtitrated with electrogenerated bromine. The titration course is recorded either amperometrically or chemiluminometrically. Hydrazine can be determined precisely and accurately in the range between 0.1 microM and 1 mM without calibration. Nitrite is reduced by hydrazine according to the reaction 2 NO2- + 2 H+ + NH2-NH2 --> N2O + N2 + 3 H2O. Applying the amperometric and the chemiluminometric end-point location nitrite was determined accurately and precisely in the ranges 0.25-65 microM and 0.10-50 microM, respectively. The method was applied to the determination of nitrite in tap and river water.

Sensitive determination of nitrite by means of a Landolt-type reaction in fluorescent aggregates of a binaphthyl-based amphiphile

The iodine quenching effect on the fluorescence of a binaphthyl-based amphiphile, C8BNC6N, was used for monitoring the Landolt-type reaction between nitrite, iodide, and thiosulfate. Due to the possibility of iodine detection in the 10−8–10−7M range, and to the effective concentration of anionic reagents on the surface of cationic aggregates, the indicator reaction can be monitored using reagents at concentration levels as low as 10−7M. To optimize the analytical system, the effect of pH and reagent concentrations on the rate of indicator reaction were studied. The influence of the matrix of water samples and effect of side-reactions increasing the value of a blank test were examined. A procedure for nitrite determination in water was developed, using the diazo reaction for selective nitrite removal to provide a reference solution, which avoided possible effects of the matrix components. The usefulness of this method was tested by determining trace amounts of nitrite in water samples. The procedure allows determination of nitrite down to 5 ng/ml (detection limit about 2ng/ml) with r.s.d. of 10% in the 20–250 ng/ml range.