Flow/sequential injection determination of gaseous ammonia with a glass diffusion denuder

A new combination of a flow/sequential injection method for the analysis of ammonia has been developed. Gaseous ammonia is selectively absorbed in a phosphoric acid coated glass tube and determined with Berthelot reagents by flow injection. The combination of the gas diffusion denuder sampler with flow injection makes this method very sensitive and selective. The limit of detection of 0.15 mug NH(3).     

The determination of hydrogen chloride in ambient air with diffusion/denuder tubes

A manual method for the determination of hydrogen chloride in air, based on diffusion/denuder tube separation from particulate chloride aerosol is described. When air is drawn through a tube coated with a selective absorbent (sodium fluoride), separation is achieved because gaseous hydrogen chloride diffuses much more rapidly to the tube walls than particulate chloride aerosol, which passes through virtually unabsorbed. After the sampling period (the length of which depends on the concentration of gaseous hydrogen chloride expected), the sorbed hydrogen chloride is washed from the tube and measured with a highly sensitive chloride ion-selective electrode with a mercury (I) chloride membrane. The method is examined theoretically and experimentally. The experimentally derived absorption efficiencies of the diffusion/denuder tubes were > 90% and the standard deviation of the method was 0.023 μg m^?3 for hydrogen chloride concentrations of 0.16–0.55 μg m^?3. Interference from particulate chloride salts was negligible; this was confirmed by tests with artificially generated aerosol particles from an aerosol generator. The diffusion/denuder tubes have high capacity; level as high as 330 μg m^?3 hydrogen chloride can be sampled for 60 min without affecting performance. A detection limit of (50/t) μg m^?3 can be achieved, where t is the sampling rime (min); e.g., 1μg m^?3 hydrogen chloride can be detected with a sampling period of 50 min.     

Use Of Diffusion Controlled Preconcentration Systems With Chemically Immobilized Coatings For The Determination Of Atmospheric Nitric Acid

Abstract

A new coating procedure for different diffusion controlled preconcentration methods (tubular denuder, annular denuder, diffusion screen) is described for the determination of nitric acid in air. In this study, a silanization reaction is applied to obtain a chemically fixed coating with an end placed functional NH₂-group, which can be used as a sink to collect acidic compounds from air. This coating must be carried out only once and can be used for a long time. The denuders, coated with this procedures, were compared with conventionally coated NaF denuders.     

Determination of ammonia and nitric acid using a diffusion denuder method

Summary A diffusion denuder technique, using annular denuders, has been introduced in our laboratory. The characteristics of different coatings for the enrichment of both ammonia and nitric acid have been determined in a laboratory study applying test atmospheres. The results, partly differing substantially from theoretical predictions, are presented here. The method has been applied for the determination of trace amounts of ammonia and nitric acid at various sites in the upper Rhine region.     

The determination of free ammonia in ambient air with diffusion/denuder tubes

Ammonia is important in atmospheric chemistry because it neutralises acidic species and increases the pH of cloud droplets. Data on the concentration of free ammonia in the atmosphere are sparse because it is difficult to separate free ammonia from particulate ammonium salt aerosol. A manual method for the determination of free ammonia in air is described based on diffusion/denuder tube separation of ammonia from ammonium salt aerosol. When air is drawn through a tube coated with a selective absorbent (here oxalic acid) separation is achieved because the gaseous species diffuses much more rapidly to the tube wall than the particles. After the sampling period (usually 1–4 h, depending on the free ammonia concentration expected), the sorbed ammonia is washed from the tube and measured potentiometrically with an ammonia probe. The method is tested theoretically and experimentally. The absorption efficiency of the coated tubes is ca. 90%. In samples of room air containing 12–28 μg m^?3, the standard deviation is estimated as 1.0 μg m^?3. In field use, ammonia contents were in the range 0.53–5.0 μg m^?3.     

Determination of C1-C3 carboxylic acids in air with diffusion controlled sampling at elevated flow rates

Summary A sampling system for the determination of C₁-C₃ carboxylic acids in air is described. Acids are collected on coated diffusion screens at elevated flow rates (5.6 L/min), and afterwards quantified by ion-chromatography. Collection efficiency, behaviour of the absorbed comounds and the penetration of particles through coated screens are reported. Results of field measurements and their comparison with those obtained with conventional tubular denuder tubes are shown.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Evaluation of denuder sampling for a mixture of three common gaseous diisocyanates

A denuder sampler has been evaluated for a mixture of three gaseous diisocyanates, i.e. toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI). Sampling was performed at a total concentration of diisocyanates close to the Swedish occupational exposure limit (OEL), which is 10 ppbv (69-92 microg m(-3)), for a 5-min period. The denuder tube was coated with a chemosorptive stationary phase consisting of SE-30 (polydimethylsiloxane) and the derivatising reagent dibutylamine (DBA). It was shown that the denuder has a collection efficiency for HDI and IPDI comparable to that of an impinger method, while sampling of TDI resulted in an 8% lower concentration. Both short-term (15 min) and long-term (8 h) sampling periods were shown to yield reproducible results. For 8-h measurements, a sampling flow rate of 5 mL min(-1) was shown to be suitable for the investigated concentration range, i.e. 10-100 ppbv (69-921 microg m(-3)). A flow rate of 25 mL min(-1) or higher resulted in breakthrough after 8 h due to chromatography of the compounds in the adsorbent. The limit of detection (LOD) for the air sampling method is nearly 500 times lower than the OEL. The denuder tubes can be prepared at least 10 days prior to sampling without degradation of performance. Furthermore, they can be stored up to 6 days in a freezer after sampling without significant loss of analytes.     

A new method for the measurement of trace amounts of HONO in the atmosphere using an air-dragged aqua-membrane-type denuder and fluorescence detection

A new method for the measurement of trace amounts of HONO has been developed. Nitrous acid in the ambient air is absorbed in an aqueous solution by an air-dragged aqua-membrane-type denuder. The absorbed nitrite is reacted with 2,3-diaminonaphthalene, and the formed 1-naphthotriazol is measured using a fluorescence method. The calibration curve of HONO shows a straight line from 0 to 4000 ppt, and the detection limit is estimated to be 8.1 ppt calculated as being three times of the base line noise. The time resolution, which is defined as the time required to become a constant value by changing from 0 to ca. 1000 ppt was 2 min. The present method is not affected by NO(2), NO, SO(2), O(3) NH(3) or mixtures of these gases and organic nitrate, organic carboxylic acids, alcohols and aldehydes. The determination results of HONO concentrations in the ambient air by the present method are in good agreement with those by the annular denuder system and the differential optical absorption method.     

Determination of hexahydrophthalic anhydride in air using gas chromatography.

Two methods for the determination of hexahydrophthalic anhydride (HHPA) in air were developed. In a solid sorbent method, HHPA was sampled in Amberlite XAD-2 tubes, eluted in toluene and analysed by gas chromatography with flame ionization detection. The sampling rates were 0.2 and 1.0 l/min. At 15 micrograms/m3 (relative humidity less than 2%) and 27 micrograms/m3 (relative humidity 70%) no breakthrough was observed. However, at 160 micrograms/m3 (relative humidity less than 2%), 6% breakthrough was found. The sampling efficiency of the sampling rates 0.2 and 1.0 l/min did not differ. In a bubbler method, HHPA was sampled in bubblers filled with 0.1 M sodium hydroxide solution. The sodium salt of hexahydrophthalic acid was formed. No breakthrough was observed using a sampling rate of 1.0 l/min. The samples were stable during storage for eight weeks in a refrigerator. The HHP acid was esterified with methanol-boron trifluoride and analysed by gas chromatography-flame ionization detection. Apparatus for the generation of standard atmospheres of HHPA, in the range of 10-3000 micrograms/m3, was developed using the diffusion principle. For the solid sorbent method the precision (coefficient of variation) of the overall method was 2-7%, and for the bubbler method 3-19% (range 15-160 micrograms HHPA/m3; relative humidity = less than 2-70%). A comparison between the two methods was performed using the standard atmosphere. The concentrations found by the solid sorbent method were 86-98% of those found by the bubbler method (range 15-160 micrograms HHPA per m3; relative humidity = less than 2-70%). In work environment air, 93% was found using the solid sorbent method relative to the bubbler method at a mean concentration of 330 micrograms/m3 (coefficient of variation = 39%; range 200-540 micrograms/m3). For both methods, concentrations greater than 3 micrograms/m3 could be quantified at 60 min sampling with a sampling rate of 1.0 l/min.     

Evaluation of Gas Phase and Particulate Components Relevant to Polar Tropospheric Processes

Abstract

The measurement of atmospheric trace components relevant to atmospheric chemistry, in gas phase and particulate matter, was carried out in the Antarctica troposphere during the Antarctic summer 1990–91. The determinations were carried out by sampling air through a diffusion denuder/filter pack sampling system, followed by extraction and analysis by ion chromatography. Through the analysis of the mass distribution of anions, an accurate and sensitive method for the measurement of several important species was provided. Results show that sulfur dioxide, nitric acid, sulfates, nitrates and other significant compounds might be well characterized, even at concentration levels as low as a few parts per trillions, thus providing a highly significant and consistent data set for the study of polar atmospheric chemistry.     

Determination of mercury in urine by ET-AAS using complexation with dithizone and extraction with cyclohexane

A precise and accurate graphite furnace atomic absorption spectrometric method for the determination of mercury in urine was developed. Samples were subjected to hydrolysis with nitric acid. Then, mercury in the sample was complexed by dithizone and extracted by cyclohexane. Mercury concentrations were determined against a urinematched calibration curve. Coated graphite notched partition tubes (Varian) and forked pyrolytic platforms (Varian) were used. The detection limit of the method (x(blank) + 3 SD(blank)) was 1 mug 1(-1). The between run precision CV's were 4.7 and 3.4% for urine with a mercury concentration of 48.2 and 156.2 mumol 1(-1), respectively; the within run precision CV's were 8.9 and 2.9% for urine with a mercury concentration of 17.0 and 172 mug 1(-1), respectively.     

Continuous chemiluminescence determination of formaldehyde in air based on Trautz-Schorigin reaction

A new continuous method for the determination of formaldehyde in air is described. A cylindrical wet effluent diffusion denuder is used for the collection of formaldehyde from air into a thin film of absorption liquid (distilled-deionized water). Formaldehyde in the denuder concentrate is on-line detected employing a chemiluminescence flow method based on a reaction of formaldehyde and gallic acid with hydrogen peroxide in an alkaline solution. The collection efficiency of formaldehyde is quantitative at the air flow rate of 0.5 L min⁻¹ (absorption liquid flow rate of 336 μL min⁻¹). The limit of detection (S/N = 3) is 0.60 μg m⁻³ HCHO (0.49 ppb). The calibration graph is linear up to 300 μg m⁻³ HCHO (244 ppb). The relative standard deviations of chemiluminescence method for 1 × 10⁻⁶ and 5 × 10⁻⁶ M HCHO are 2.87% and 1.49%, respectively. Acetaldehyde interferes negligible, other compounds do not interfere. The method was employed for formaldehyde measurement in ambient air. The comparison measurement illustrates the good agreement of results obtained by proposed method with those obtained by reference fluorimetric method.     

Wet effluent parallel plate diffusion denuder coupled capillary ion chromatograph for the determination of atmospheric trace gases

We describe an inexpensive, compact parallel plate diffusion denuder coupled capillary IC system for the determination of soluble ionogenic atmospheric trace gases. The active sampling area (0.6x10 cm) of the denuder is formed in a novel manner by thermally bonding silica gel particles to the surface of Plexiglas plates. The effluent liquid from the parallel plate diffusion denuder is collected and preconcentrated on a capillary preconcentrator column before analysis using a capillary ion chromatograph. Using SO(2) as the test gas, collection efficiency is essentially quantitative at air sampling rates up to 500 ml min(-1). The system provides a limit of detection (LOD) of 1.6 parts per trillion for SO(2) for a 10 min sampling period.     

A Gaseous Nitric Acid Analyzer for the Remote Atmosphere Based on the Scrubber Difference/NO-Ozone Chemiluminescence Method

An in situ nitric acid analyzer has been designed for sensing in the remote atmosphere. Its operation is based on measuring the concentration difference between the total odd nitrogen species (NO(y)) and HNO(3)-scrubbed NO(y). NO(y) was measured by an NO-ozone chemiluminescent detector equipped with a molybdenum converter. A temperature-controlled annular denuder coated with NaCl was used as a scrubber of gaseous HNO(3). The current detection limit of the HNO(3) analyzer was estimated to be 158 and 71 pptv (parts per trillion by volume) with an integration time of 2 and 10 min (2sigma), respectively. The analyzer was calibrated using standard gaseous HNO(3) to verify its performance. The HNO(3) concentrations measured by the scrubber difference and the NO-ozone chemiluminescence methods (SDCL method) were in agreement with those obtained by the denuder method within the experimental uncertainties (more than +/-4%). We conducted limited field observations of NO(y) and HNO(3) in the remote atmosphere using the newly designed SDCL method at Cape Hedo, Okinawa, Japan.     

Determination of nitrous acid in air using wet effluent diffusion denuder-FIA technique

A sensitive and fast method for the determination of nitrous acid (HONO) in air is described. The method combines a continuous collection of nitrous acid into a thin film of absorption liquid in a cylindrical wet effluent diffusion denuder (CWEDD) and on-line analysis of collected nitrous acid at the denuder concentrate employing a flow-injection analysis (FIA) where nitrous acid is oxidized into peroxynitrous acid and a chemiluminescent light emitted during the reaction of peroxynitrite with luminol is detected. Various absorption solutions (carbonate, bicarbonate, phosphate) as well as deionized water were compared from point of view of collection efficiency of nitrous acid at the CWEDD and selectivity and sensitivity of nitrous acid determination in air.All tested liquids provide quantitative collection of HONO in the CWEDD at the air flow rate of 1 L min⁻¹. The detection limit of nitrous acid of 15 ppt (v/v) is the same for all tested liquids. Small positive interference of nitrogen dioxide and peroxyacetylnitrate has been found. The lowest interference of NO₂ was found for 1 × 10⁻⁴ M NaHCO₃ (pH 6.4; 0.18%) while for deionized water interference of NO₂ (0.28%) was slightly higher. The lowest interference of peroxyacetylnitrate was found for deionized water (1.46%). No enhanced formation of HONO inside the cylindrical wet effluent diffusion denuder was observed for simultaneous bringing of nitrogen dioxide together with phenol, p-cresol, guaiacol, catechol, o-nitrophenol as well as with n-octane, n-nonane, n-decane, isoprene, α-pinene, β-pinene, camphene, 3-carene, α-phellandrene, S-limonene, benzene, toluene or o-xylene in comparison with formation of HONO only in the presence NO₂.Deionized water was chosen as the optimum absorption liquid for the sampling of atmospheric nitrous acid at the CWEDD as well as for FIA chemiluminescent detection. The time resolution is 70 s and the response time is 164 s. The calibration curve is linear over 4 orders of magnitude (0.045-450 ppb HONO). The CWEDD-FIA technique has been applied to the measurement of nitrous acid in urban air.     

Wet effluent diffusion denuder technique and determination of volatile organic compounds in air. I. Oxo compounds (alcohols and ketones)

The wet effluent diffusion denuder (WEDD) preconcentration technique for the determination of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 1-pentanol, acetone, methyl ethyl ketone, diethyl ketone and methyl n-propyl ketone in air is discussed. The compounds are continuously collected into a thin film of deionized water flowing down the inner wall of the cylindrical wet effluent diffusion denuder. The concentrate is analysed by gas chromatography. Detection limits of alcohols and ketones are as low as 1 microg/l (GC-flame ionization detection) and/or 1 ng/l (GC-MS). This technique could be applicable for the continuous monitoring of ppb (v/v) levels of both alcohols and ketones in the air.     

Application of the denuder technique in filter sampling of airborne chromates at ground level concentrations

The use of the denuder technique for the preserving sampling of chromium(VI) in airborne dust at ground level (immission) concentrations was investigated. A simple denuder with activated charcoal retained by a steelwire-net cylinder was constructed. The sorption abilities of the denuder towards sulfur dioxide, which is responsible for the reduction of sampled Cr(VI) on the filter surface, were examined under various conditions. The measurements provide evidence for a laminar flow inside the denuder. At a flow rate of 100 L/h and a temperature of 27 °C the theoretical sorption value of 99.6% is reached within an experimental error of ±0.1%. A relative humidity of 19–91.5% has no influence on the sorption. In order to check if an experimental sorption value of 99.5% is sufficient to stabilize Cr(VI) on the filter surface, sampling was simulated by sucking SO₂-loaded air through Teflon filters loaded with Cr(VI) containing aerosol particles with diameters of about 0.3 m. Aerosols of two different compositions were generated by a sprayer in combination with a diffusion dryer. The particle size distributions were determined from scanning electron microscopic pictures. Chromium(VI) was eluted from the filters with an alkaline buffer and extracted from the filter eluates with a solution of a liquid anion exchanger. Chromium was determined with graphite furnace atomic absorption spectrometry. The Cr(VI) losses are between 57 and 16% depending on the composition of the aerosol particles and the sampling time. Realistic conditions were chosen regarding the initial Cr(VI) on the filters and the amount of sulfur dioxide which passed through the denuder.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Feinreinigung von Radiostrontiumproben mittels Ionen-Chromatographie

Summary An annular denuder system for simultaneous determination of gaseous and particulate pollutants in ambient air was developed. Inorganic acids (HCl, HNO₃) were collected in a NaF-coated denuder, while organic acids (HCOOH, CH₃COOH) were trapped in one coated with KOH. NH₃ was sampled with a H₃PO₄-coated denuder tube. Particulate H₂SO₄ was evaporated at elevated temperature (145°–155°C) and deposited on a NaF-coating together with HCl and HNO₃ originating from thermal decomposition of NH₄Cl and NH₄NO₃. NH₃ resulting from deammoniation of (NH₄)₂SO₄ as well as NH₃ remaining from NH₄Cl and NH₄NO₃ were collected in a H₃PO₄-coated denuder. The practical collection capacity of the tubes ranged from 0.35 to 1.0 mol calculated from an experimentally determined sorption efficiency of at least 90%. The precision, expressed as relative standard deviation, of sampling and analytical procedures was determined from duplicate measurements in ambient air. The reproducibility varied from 9% to 14% for the gaseous components, while that of the particulate compounds ranged from 12% to 23%. Aqueous extracts of the denuder coatings were analysed for ionic components by ion chromatography using conductivity detection. The minimum detectable concentration in air was found to be 1.5 to 14 nmol/m³ for the different compounds calculated for 1.6 m³ sample volume, based on 3-h measurements at a flow of 9 l/min.

---

Bestimmung der atmosphärischen Konzentrationen von anorganischen und organischen gasförmigen Säuren, NH₃, teilchenförmigem SO ₄ ^2– , NO ₃ ^2– und Cl^– mit einem Ringspaltrohr-Diffusionsdenudersystem

---

On leave from the Institute of Occupational Health, Helsinki, Finland     

Annular denuder tube preconcentrator for nitrobenzene determination by gas chromatography with electron-capture detection

A platinum/lead alloy-coated annular denuder tube was employed to concentrate nitrobenzene from nitrogen atmospheres of relative humidity < 5% at ambient temperatures. The limit of detection achieved was 1.7 ng of nitrobenzene, which could be obtained from a concentration of 0.15 μg m^?3 of nitrobenzene in nitrogen. Quantification was carried out at concentrations above 0.12 μg m^?3 of nitrobenzene in nitrogen over a 4-month period, although ageing and deterioration of the denuder system were noted, necessitating regular recalibration. The results support claims made elsewhere regarding the suitability of denuder tubes for organic vapour determination, in this instance with an analyte-selective collection surface.     

Determination of total gaseous selenium in atmosphere by honeycomb denuder/differential pulse cathodic stripping voltammetry

A new analytical method has been developed for the determination of total gaseous selenium in the atmosphere by honeycomb denuder collection followed by differential pulse cathodic stripping voltammetry (DPCSV) measurement. Gaseous selenium was collected in a denuder coating solution containing 2% HNO(3) and 2% glycerine. The soluble product, selenious acid, was then extracted by water for DPCSV analysis. The collection efficiency for gaseous selenium was 99.1% at a flow rate of 1 l min(-1) for 3 h. Excellent linearity in DPCSV was maintained up to Se concentration of 40 ng ml(-1). This was equivalent to a working concentration of 220 ng m(-3) of selenium in the atmosphere. A precision of 1.26% RSD (n=5) for 5 ng Se was obtained, and the detection limit (3sigma) and the quantitative determination limit were estimated to be 0.96 and 3.19 ng m(-3). The average recovery of selenium in three standard samples prepared by independent digestion of NIST SRM 1648 (Urban Particulate Matter) using our analytical system was 99.0%. The total content of gaseous selenium in the atmosphere of our laboratories was 3.2-4.4 ng m(-3).