Studies on the adsorption of nitrogen dioxide onto manganese dioxide-coated quartz piezoelectric crystals

A technique for obtaining thin; evenly distributed manganese dioxide coatings by melting manganese nitrate is outlined. Responses of an AT-cut quartz piezoelectric crystal coated with manganese dioxide to nitrogen dioxide (12.5-10 000 μl 1^?1) over a range of humidities (400–4,800 μ1 l^?1 water) and temperatures (20–35 °C) are given. The response of the simulated product manganese nitrate, over the same range of humidities, is evaluated in relationship to real product formation. The approach may be applicable to other metal salt/metal oxide systems. The detection limit is 7 μl^?1 nitrogen dioxide.     

A galvanic solid-state sensor for monitoring ozone and nitrogen dioxide

The sensor is based on silver and platinum electrodes with an intervening silver iodide disk as a solid electrolyte. The small disk (13 mm diameter) is easily made by pressing (7000 kg cm^-2) silver powder, silver iodide and a platinum gauze in layers in a die. The detector cell containing the disk is thermostated at 120 ± 0.1°C. When sample gas at 30 ml min^-1 impinges on the platinum cathode, the current flowing in the external circuit is linearly related to the concentration of ozone and/or nitrogen dioxide up to 0.5 ppm from the detection limit of 0.5 ppb for ozone or 1 ppb for nitrogen dioxide.     

Laboratory and field measurements of a badge type passive sampler for the determination of ambient sulfur dioxide concentrations

The performance of a badge type passive sampler for the determination of sulfur dioxide is described. The trapping agent is triethanolamine. Analysis is performed by ion chromatography. Thus, the method allows the simultaneous detection of sulfur dioxide and nitrogen dioxide. The sampler was tested in the laboratory and in the field. The intercomparison with independent methods in the field showed very good agreement against two active sampling methods. Regression analyses (the results of the passive sampler always represent the y-axes) gave r² = 0.81 and k = 1.07 ± 0.01 for the intercomparison with an annular denuder technique and r² = 0.92 and k = 0.96 ± 0.01 for the intercomparison with a commercial fluorescence sulfur dioxide analyzer. The average reproducibility in the field was 7% (RSD). The detection limit was 0.18 μg SO₂/m³ for an exposure time of two weeks. Received: 9 February 1998 / Revised: 22 June 1998 / Accepted: 26 June 1998     

Laboratory and field measurements of a badge type passive sampler for the determination of ambient sulfur dioxide concentrations

The performance of a badge type passive sampler for the determination of sulfur dioxide is described. The trapping agent is triethanolamine. Analysis is performed by ion chromatography. Thus, the method allows the simultaneous detection of sulfur dioxide and nitrogen dioxide. The sampler was tested in the laboratory and in the field. The intercomparison with independent methods in the field showed very good agreement against two active sampling methods. Regression analyses (the results of the passive sampler always represent the y-axes) gave r² = 0.81 and k = 1.07 ± 0.01 for the intercomparison with an annular denuder technique and r² = 0.92 and k = 0.96 ± 0.01 for the intercomparison with a commercial fluorescence sulfur dioxide analyzer. The average reproducibility in the field was 7% (RSD). The detection limit was 0.18 μg SO₂/m³ for an exposure time of two weeks. Received: 9 February 1998 / Revised: 22 June 1998 / Accepted: 26 June 1998     

Ultraviolet laser photoacoustic spectrometric determination of sulfur dioxide in mixtures containing larger amounts of nitrogen dioxide

Concentrations of sulfur dioxide in the nl l^?1 range are quantitatively measured in gaseous mixtures containing a large excess of nitrogen dioxide by using ultraviolet laser photoacoustic spectrometry. Mixtures containing SO₂ as a minority component are prepared by gas permeation methods. Photoacoustic spectra with 0.5 cm^?1 resolution in the 299.7–303.1 nm region are presented and are used to identify the spectral signatures of each component needed for selective detection. A procedure for the determination of both SO₂ and NO₂ is presented with major emphasis on the sensitivity and dynamic range of SO₂ detection. Concentrations of SO₂ as low as 1.45 nl l^?1 are detected in the presence of 901 nl l^?1 NO₂ in nitrogen at 1 atm total pressure. The effect of adding water vapor (from 17 to 66% relative humidity) is described.     

Tapioca Biofilm Containing Nitrogen‐doped Titanium Dioxide Nanoparticles for Electrochemical Detection of 17‐β Estradiol

A novel sensor architecture based on thin film of tapioca decorated within nitrogen‐doped titanium dioxide (N‐TiO₂) nanoparticles is reported. The nanostructures were characterized by scanning electron microscope, transmission electron microscope, X‐rays diffraction and voltammetric techniques. The proposed electrode was used for detection of low concentrations of 17‐β estradiol in without purification step, which was investigated by using linear sweep adsorptive stripping voltammetry. Under optimal conditions, the analytical curve was linear over a 17β‐estradiol concentration range of 9.9×10⁻⁶ to 1.4×10⁻⁵ mol L⁻¹, with a detection limit of 1.7×10⁻⁷ mol L⁻¹. The tapioca and N‐TiO₂ nanoparticles homogeneous film was applied for detection of 17‐β‐estradiol in tap water and synthetic urine samples, which presented satisfactory results.     

Kinetics of the reaction between 1,3-diphenylisobenzofuran and nitrogen dioxide studied by steady-state fluorescence

1,3-Diphenylisobenzofuran (DPBF) is a fluorescent molecule which is believed to react highly specifically toward reactive oxygen species such as singlet oxygen (¹O₂), hydroxy (HO^·), alkyloxy (RO^·), and alkylperoxy (ROO^·) radicals. In all cases the reaction product is 1,2-dibenzoylbenzene. In order to prove that DPBF gives the same product in contact with reactive nitrogen species, its reaction with nitrogen dioxide radical has been studied in 2,2,4-trimethylpentane using the steady-state fluorescence method and mass spectrometry. The progress of the studied reaction was measured by observation of changes in fluorescence intensity of DPBF after addition of nitrogen dioxide (NO₂). The rate constants of DPBF fluorescence decay affected by NO₂ have been determined. Experiments were conducted over the temperature range of 13–37 °C and for NO₂ concentrations from 0.02 to 0.14 mmol dm^?3. It has been found that the reaction between 1,3-diphenylisobenzofuran and nitrogen dioxide proceeds in two steps. The first step is a very rapid reaction whose rate could not be measured under established experimental conditions. The second step is slower. The reaction product was identified by registration of mass spectra. The probable reaction mechanism is proposed.     

Rapid,automatic, high-precision method for micro,ultramicro, and trace determinations of sulfur

Samples are burned in a Carlo Erba 1106 elemental analyzer over copper oxide with oxygen, injected into the carrier gas. Combustion gases are reduced with copper. Water is absorbed, and sulfur dioxide is separated from carbon dioxide and nitrogen in a very short column of Porapak QS. Sample size is upt ot 0.7 mg, one determination takes 5 min, and the sampler takes up to 196 samples. It can be continuously loaded, and the instrument can be left to work automatically overnight. For the micro determination, helium is the carrier gas, and sulfur dioxide is measured with a thermal conductivity detector. The standard deviation of 18 analyses of pure organic compounds was 0.0446% S. The detection limit is 0.5 μg S, or about 0.1% S in a normal 0.5-mg sample. For ultramicro and trace determination, nitrogen is the carrier gas, and the measurement is made with an electron capture detector. The detection limit is 0.002 μg S, or about 0.0004% (4 mg kg^?1 S) in a normal 0.5-mg sample.     

A galvanic gas sensor using poly (ethylene oxide) complex of silver trifluoromethane sulphonate electrolyte

Summary A galvanic sensor for monitoring nitrogen dioxide was developed by using a poly(ethylene oxide) complex of silver trifluoromethanesulphonate electrolyte. The sensor, which is expressed as Au/P(EO)_4.5 AgCF₃SO₃/Ag, is a small disk (i.d. 13 mm). The polymeric electrolyte film was made by casting the mixture of acetonitrile solutions of both P(EO) (MW 6×10⁵) and AgCF₃SO₃. The working electrode was made by sputtering of gold in argon. The thicknesses of the desposited gold, polymeric electrolyte film and silver are 25 nm, 30 m and 1 mm, respectively. When the sample gas containing nitrogen dioxide impinges at 20 ml min^–1 on the gold cathode, the current flowing in the external circuit was linearly related to the concentration of nitrogen dioxide from 20 ppb to about 10 ppm. The current efficiency of the cell was 0.051%. The cell's response time was about 2 min for 0.5 ppm of nitrogen dioxide.     

Development and optimization of a lab-on-a-chip device for the measurement of trace nitrogen dioxide gas in the atmosphere

We propose the use of lab-on-a-chip technology for measuring gaseous chemical pollutants, and describe the development of a microchip for the detection of nitrogen dioxide (NO2) in air. A microchip fabricated from quartz glass has been developed for handling the following three functions, gas absorption, chemical reaction and fluorescence detection. Channels constructed in the microchip were covered with porous glass plates, allowing nitrogen dioxide to penetrate into the triethanolamine (TEA) flowing within the microchannel beneath. The nitrogen dioxide was then mixed with TEA and reacted with a suitable fluorescence reagent in the chemical reaction chamber in the microchip. The reacted solution was then allowed to flow into the fluorescence detection area to be excited by an ultraviolet light-emitting diode (UV-LED), and the fluorescence was detected using a photomultiplier tube (PMT). The reaction time, reagent concentration, pH, flow rate and other measurement conditions were optimised for analysis of nitrogen dioxide in air. Preliminary studies with standardized test solutions revealed quantitative measurements of nitrite ion (NO2-), which corresponded to atmospheric nitrogen dioxide in the range of 10-80 ppbv.     

Thermal lens spectrophotometry of nitrogen dioxide using an excimer-laser-pumped dye laser

A thermal lens spectrophotometer based on a pulsed dye laser pumped by an excimer laser was constructed. A thermal lens spectrum was measured for nitrogen dioxide by scanning the dye laser wavelength, which was well correlated with an absorption spectrum. A linear calibration graph was obtained in the nl 1^?1 range, the detection limit being 4 nl 1^?1, which is similar to the best value achieved by other laser spectrometric methods. The enhancement factor achieved was 16, which is much smaller than the theoretical value of 292 calculated by assuming an exciting laser with a single transverse mode (beam waist radius 0.12 mm). However, the observed enhancement factor agrees fairly well with the theoretical value of 17 calculated from the observed beam radius (0.5 mm) at the waist. Hence the observed small enhancement factor is ascribed to poor beam quality of the dye laser used. Pulsed thermal lens spectrophotometry is shown to be useful especially for the analysis of gaseous samples at elevated temperatures.     

A new method for atmospheric nitrogen dioxide measurements using the combination of a stripping coil and fluorescence detection.

A new stripping coil for the collection of nitrogen dioxide (NO2) has been developed to increase its versatility and efficiency. Nitrogen dioxide measurements based on quantitative collection through a reaction coil into an alkaline solution has been examined. Nitrogen dioxide is collected in a 0.1 N NaOH solution. This collection system has an efficiency of nearly 100%. The absorbed nitrogen dioxide has been measured by fluorescence detection with sub-ppbv detection limits. The excitation wavelength at 360 nm and the produced emission wavelength at 405 nm were suitable for nitrite ion measurements.     

Aminophenyl Benzimidazole as a New Reagent for the Estimation of NO2/Nitrite/Nitrate at Trace Level: Application to Environmental Samples

Abstract

A simple and sensitive spectrophotometric method for the determination of nitrogen dioxide in ambient air and nitrite/nitrate in water and soil samples has been developed. Nitrogen dioxide in air has been fixed as nitrite ion using alkaline sodium arsenite as absorbing medium. The method is based on the reaction of nitrite with aminophenyl benzimidazole in acid medium to form diazonium ion, which is coupled with N‐(1‐naphthyl)ethylenediamine dihydrochloride to form an azo dye with an absorption maximum at 555 nm in aqueous phase. The method obeys Beer's law in the concentration range 0–10 µg of nitrite in 25 ml solution. The molar absorptivity has been found to be 6.3×10⁴ l mol^?1 cm^?1. The dye can be extracted quantitatively into isoamyl alcohol under alkaline condition and the addition of methanolic hydrochloric acid restores the original dye colour. Beer's law is obeyed in the concentration range 0–2 µg of nitrite with a detection limit of 0.009 µg. The effect of interfering species has been studied and the developed method has been applied to determine trace levels of nitrogen dioxide in ambient air and the results have been compared with the standard method. It is also applied to measure the nitrite/nitrate levels of surface and ground water samples collected from lakes, tube wells as well as soil samples.     

Improvement of a monitoring tape for nitrogen dioxide in air

A porous cellulose tape containing a silica gel that was previously impregnated with a processing solution containing p-toluenesulfonic acid, sulfanilic acid, N-1-naphthyl ethylene diamine dihydrochloride, ethylene glycol and methanol has been developed to provide a highly sensitive detection of nitrogen dioxide in air. When the sample including nitrogen dioxide was passed through the tape, the color of tape changed to red, and the degree of color change could be recorded by measuring the intensity of reflecting light (555 nm). The calibration graph was linear up to approximately 0.10 ppm. The detection limit was 0.5 ppb for nitrogen dioxide with a sampling time of 8 min and a flow rate of 60 ml min(-1). No interferences were observed from ammonia (40 ppm), sulfur dioxide (51 ppm), carbon dioxide (21%), ozone (0.75 ppm), hydrogen sulfide (27 ppm) or nitrogen monoxide (99 ppm).     

A new fluorescence method for determination of ozone in ambient air

A new simple method for determination of ozone in ambient air is presented. The reaction employed is based on the known ozonolysis of indigo dye. The indigotrisulfonate molecule contains one carbon–carbon double bond (C═C), which reacts with ozone and generates isatinsulfonates and sulfoanthranilate. The quantitatively formed sulfoanthranilate presents fluorescence (λ_ex 245 nm, λ_em 400 nm). Ozone was collected using two cellulose filters coated with 40 μL of 1.0 × 10^{− 3} mol L^{− 1} of indigotrisulfonate. The analytical response was linear in the range 0–150 ppbv ozone, and a detection limit of 7 ppbv was achieved using a sampling time of 15 min and an optimum sampling air flow rate of 0.4 L min^{− 1}. There was no interference from sulfur dioxide, formaldehyde or nitrogen dioxide. The ozonolysis mechanism and the reaction products are discussed.     

Applicability of microwave induced plasma optical emission spectrometry (MIP-OES) for continuous monitoring of mercury in flue gases

The applicability of microwave-induced plasma optical emission spectrometry (MIP-OES) for continuous monitoring of the environmentally hazardous element mercury in flue gases has been studied. Microwave induced plasmas have been sustained using both a TM₀₁₀ cavity (Beenakker resonator) and a so-called Surfatron. The analytical figures of merit for mercury in argon and helium discharges with both types of low-power micro-wave discharges have been examined. To determine mercury in artificial stack gases non-mixed argon/nitrogen discharges have been tested using a tangential flow torch design which allows to introduce a metal-loaded nitrogen gas flow as external gas and argon as internal gas. The addition of main flue gas components such as water vapour (concentration <6 g/m³), oxygen (<4% v/v) and carbon dioxide (<15% v/v) decrease the mercury line intensities to a considerable extent. Trace gases (CO, HCl, SO₂, NO) in concentrations typical to waste incineration processes have been found to have no effect on the mercury and the argon line intensities. The detection limit of mercury in nitrogen is 8 g/m³ using the TM₀₁₀ MIP and 10 g/m³ using the Surfatron. As such low detection limits are below the emission limit values of present-day environmental legislation MIP-OES is useful for on-line monitoring of mercury.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Development of a Passive Sampler for Long-Term Measurements of Formaldehyde and Total Oxidants in Air

A diffusive sampling device is described that is capable of reliable measurements of formaldehyde and total oxidants (Ox = ozone + nitrogen dioxide) at sub-ppbv concentration levels in ambient air. These species are collected on silica gel particles coated with 1-methyl-1-(2,4-dinitrophenyl)hydrazine (MDNPH) and phosphoric acid. The formaldehyde hydrazone (HCHO-MDNPh) and the N-methyl-2,4-dinitroaniline (MDNA) formed are extracted with acetonitrile and determined by HPLC with UV detection at 365ánm. The measured sampling rate for HCHO, 15.0 mLmin^-1, agrees well with the theoretical value of 16.0, whilst an experimental sampling rate of 10.7 mLmin^-1 (25% lower than the calculated one) is observed for Ox. The sampling rates seem to be independent of the sampling duration up to one month. The precision of the measurements for co-located passive samplers averaged is 7.3% for HCHO and 7.2% for Ox in urban air.     

Spectrophotometric Determination of Nitrogen Dioxide <Nitrite>

Abstract

A highly sensitive spectrophotometric method has been developed for the determination of nitrogen dioxide (nitrite as NO_z ^?) by reacting manganese dioxide in 1:20 perchloric acid. An amount of manganese dioxide (MnO_z) equivalent to the concentration of nitrogen dioxide becomes soluble due to the reduction of Mn (IV) to Mn (II) by nitrite in acidic medium. The soluble Mn (II) ion is filtered to remove excess of MnO₂ and is oxidized to permanganate ion by periodic acid in presence of phosphoric acid. The violet colored solution shows maximum absorbance at 525 nm. The sensitivity of the method is 0.08 ppm based on 0.0044 absorbance, and Beer's law is obeyed in the concentration range of 0.2 to 10.0 μg/mL of NO₂ ^?. Molar absorbance is found to be 2442 at 525 nm.

In the present investigation NO₂ ^? was treated with excess of MnO₂ in 1:20 perchloric acid where NO₂ ^? reduces equivalent amount of Mn (IV) to Mn (II) and becomes soluble. The soluble Mn (II) was heated to boiling and 25 mg (approx.) periodic acid is added and cooled. The volume of each solution is made to 50 mL in volumetric flask. Reagent blank is prepared in similar way except sodium nitrite solution. The absorbance is measured at 525 nm against reagent blank.     

Fluorometric Determination of Nitrogen Dioxide in Atmosphere Sampled by the Liquid Droplet Technique

A new, simple, sensitive and selective fluorometric method for the determination of nitrite has been developed. The reaction of nitrite with hydralazine in acidic medium, heated on a boiling water-bath for 15 min, produced a tetrazolo (5,1-a) phthalazine (Tetra-P). The product formed was measured at _ex = 274 nm and _em = 345 nm. The fluorescence intensity was valid over a nitrite concentration range 0.067–60.3 ng mL^–1, with a detection limit of 0.0091 ng mL^–1. The reproducibility of the proposed method was determined by running a different concentration of nitrite, 13.4, 33.5, and 46.9 ng mL^–1. The % recoveries and the relative standard deviations were found to be 100.6 ± 0.9, 99.9 ± 0.5, and 99.4 ± 1.1%, respectively. The proposed method was applied successfully to the determination of nitrogen dioxide sampled from the atmosphere using the liquid droplet method. The nitrogen dioxide our wind tunnel was controlled by an NO _x analyzer based on a chemiluminescence analyzer detector (CLAD 1000). A linear graph was obtained for the nitrogen dioxide in the wind tunnel vs. NO₂ sampled by the liquid droplet method. The effect of interference substances in the determination showed that cations and anions did not disturb the process. The results obtained were satisfactory when compared with the reference method.     

Emissionsspektrographische bestimmung von Stickstoffspuren über die Cyanbandenemission in AIIIBV-Halbleitern

Traces of nitrogen in GaP and GaAs are determined by an emission spectrographic method. The nitrogen, which is bound in the powder samples as nitride, reacts with the carbon of the powder mixture at the temperatures of the a.c. arc to form the CN-radical. The CN-band at 388.4 nm (head of the band) and the Sc I atomic line at 390.7 nm (standard) are used for the analysis. The detection limit (3s-criterion) is 100 ppm nitrogen (500 ng) in 5 mg of A^IIIB^V-semiconductor sample.