The sampling of hydrogen fluoride in air with impregnated filter paper

A method isproposed for the quantitative collection of hydrogen fluoride in air by drawing a known quantity of the air through filter paper impregnated with solutions of potassium hydroxide and glycerol or triethanolamine. Somu possibilities and limitations of the method are discussed.     

The sampling of hydrogen sulfide in air with impregnated filter paper

A method is proposed for the quantitative collection of hydrogen sulfide in air on impregnated filter paper. An aqueous solution of potassium hydroxide, potassium zincate and glycerol is used as impregnating fluid. The stability of the collected sulfide and the efficiency of collection at different humidities, temperatures, hydrogen sulfide concentrations and air velocities were determined.     

Determination of sulfur dioxide in air

The determination of sulfur dioxide in air is based on a preliminary purification with a cellulose filter and 80% isopropanol and absorption of sulfur dioxide by means of two midget impingers in 0.3 N hydrogen peroxide. The formed sulfate is titrated in an aliquot with 0.005 M barium perchlorate employing Chlorophosphonazo III (CPA) as an indicator. The method is suitable for 0.3–19.0 mg of sulfur dioxide per 50 liters of air. The standard deviation of the titration is ±0.02 ml per consumption of 5.00 ml and is four times smaller than that of the Thorin method.     

Pneumatoamperometric determination of sulfur dioxide in air on ppb level

A simple device for the determination of sulfur dioxide at ppb concentrations in air is described. The device is composed of an enrichment unit operating continuously on the basis of gas extraction into polydisperse aerosol of a liquid transferring sulfur dioxide from liter amount of air into microliter amount of liquid. The analyte is determined pneumatoamperically from the concentrate on a gold-plated porous Teflon electrode. The detection limit is 0.3 ppb (v), i.e. 0.87 microgram/m3 of sulfur dioxide, the linear range covers several orders of magnitude. The analytical response is obtained few tenths of seconds after the gas contaminated with sulfur dioxide has entered the enrichment unit.     

顺序注射化学发光联用技术测定空气中的SO2

基于在酸性溶液中SO32-被Ce4 氧化成SO42-产生很强的化学发光的原理,将顺序注射(SI)进样和化学发光(CL)检测方法联用,以0.012%三乙醇胺作吸收液,成功地测定了空气中的SO2。其浓度与发光信号强度在6.40×10-9～1.28×10-5mol/L范围内呈线性关系。方法的检出限(3σ)为4.80×10-9mol/L,对3.20×10-7mol/L的SO32-溶液9次测定的相对标准偏差为2.9%,方法回收率为98.45～103.6%。分析频率为90样/h。     

Fixation of XAD-4 power on filter paper using methyl cellulose for the passive air sampling of semi-volatile organic compounds in indoor air

The sorption capacity of a substrate serving as sampling medium can be enhanced by adding another sorbent to its surface. This is usually achieved through an impregnation process by repeated dipping of the substrate in a slurry solution containing the powder of the sorbent. Because the impregnation process only deposits the sorbent powder on the surface of the substrate, the powder could detach and fall off during field deployment. In this study, a novel approach was explored to fix the added sorbent powder to the surface of the substrate. Methylcellulose (MC) in fine crystal form was selected as the fixing agent to secure the powder of polystyrene-divinyl benzene copolymer resin (XAD-4), with its high sorption capacity, to a cellulose filter paper (CFP). The process involved first mixing XAD-4 and MC in the presence of water to form a milky slurry solution that was then painted on to the surface of the paper and then allowed to dry. The painting technique resulted in a good reproducibility of the applied amount of XAD-MC mixture with a relative standard deviation (RSD) of 12% (n = 5). Scanning electron microscope (SEM) images showed that the XAD-4 powder was held to the surface of the filter paper. No free XAD powder was dislodged from the coated filter paper when coated paper was flicked with a finger. For use as an indoor passive air sampler (PAS), this new sampling medium was placed in a round housing made of electronically polished aluminium material and was tested for uptake of polybrominated diphenyl ethers and phthalic acid dialkylesters. Surface area specific uptake rates (ASUR) of PBDEs ranged from 1.14 to 2.82 m³/(dm²d), while ASUR of phthalates had a wider range from 2.74 to 5.66 m³/(dm²d).     

The effects of sampling materials selection in the collection of reduced sulfur compounds in air

In this study, the analytical bias in the measurements of reduced sulfur compounds (RSC) was investigated in terms of sorptive loss caused by the materials selected for the sample introduction. For the purpose of this study, three vacuum samplers made in the combination of different vacuuming efficiencies (e.g., rapid versus slow sampling) and different materials (i.e., Teflon versus stainless steel (SS)) were tested to evaluate the sampling recovery rate (RR) for five RSCs: H₂S, CH₃SH, DMS, CS₂ and DMDS. To make a parallel comparison of RR, the RSC standard samples contained in one bag were transferred to another bag using each sampling system. Their relative contents between, before, and after the transfer were then evaluated between different samplers to assess the sampling bias caused by the interaction between RSC and the sampling material. In the case of the most reactive compound, H₂S, the sampling loss from the SS inlet line amounted to as high as 45%, while that for the Teflon counterpart was almost insignificant. When the sampling time was arbitrarily elongated (i.e., use of a slow sampler), the sampling loss rate of the SS inlet sampler became more significant with the RR values dropping down from 55 to 70%, across different RSCs. The overall results of our comparative study indicate that the sampling system for the reactive gaseous compounds should be checked for the material feasibility to guarantee sufficient analytical reliability.     

Spectrophotometric determination of sulfur dioxide in air, using thymol blue

A simple and sensitive spectrophotometric method was developed for the determination of trace amounts of sulfur dioxide. The method is based on the reaction of SO2 with a known excess of ICI as the oxidant. The unreacted ICI iodinates thymol blue under acidic conditions. The lambdamax of thymol blue is at 545 nm under acidic conditions, and on lodination lambdamax shifts to 430 nm. This shift results in a decrease in the absorbance at 545 nm. The amount of uniodinated thymol blue present depends on the concentration of unreacted ICI, which in turn depends on the SO2 concentration. The system obeys Beer's law in the range 0-30 microg SO2 in a final volume of 25 mL, having a molar absorptivity of 3.2 x 10(4) L/mol cm with a relative standard deviation (RSD) of 2% at 24 microg SO2 (n = 10). The uniodinated dye can be extracted into 5 mL isoamyl alcohol under acidic conditions for measurement of absorbance. The extraction method obeys Beer's law in the range 0-5 microg SO2, having a molar absorpitivity of 4.16 x 10(4) L/mol x cm with an RSD of 1.9% at 4 microg SO2 (n = 10). The method has been successfully applied to the determination of atmospheric SO2.     

Flow injection determination of gaseous sulfur dioxide with gas permeation denuder-based online sampling and preconcentration

A simple and novel flow injection method for the determination of gaseous SO(2) is described based on gas permeation denuder (GPD) online sampling and preconcentration. The GPD is easily prepared with poly(vinylidene) difluoride microporous membrane as gas permeable material and two Perspex blocks with smooth and flat interface and rectangular engraved channels of mirror image. The sample gas is on one side of the membrane and phosphate buffer of pH 7.0 as the absorbing solution is on the other side. Gaseous SO(2) permeates partially through the gas permeable membrane and dissolves in the absorbing solution. After preconcentration for 5.0 or 8.0 min, the solution is injected into the flow of 5.0 x 10(-4) mol L(-1) 5,5'-dithiobis(2,2'-dinitrobenzoic acid) (DTNB) in 0.025 mol L(-1) phosphate buffer. The resulting product formed between DTNB and absorbed SO(2) is spectrophotometrically monitored at 410 nm with a charge coupled device (CCD) fiber optic spectrometer. The calibration graphs for preconcentration of 5.0 and 8.0 min are linear up to 4.0 and 3.2 mg m(-3) with detection limits of 50 and 35 micro g m(-3), respectively. The corresponding analysis speeds are 8.5 and 6 samples h(-1). The method is selective and just suffer from interference of hydrogen sulfide at higher than 1% of SO(2) level (in m/V) with an error >+10%. The assay just uses cheap and common membrane and reagents and shows potential application in the monitoring of atmospheric SO(2).     

On-line determination of trace sulfur dioxide in air by integrated microchip coupled with fluorescence detection

A microchip-based method was developed for on-line determination of trace sulfur dioxide (SO₂) in air. Gaseous SO₂, which diffused through the porous glass materials on the microchip, was absorbed into an absorption solution of triethanolamine (TEA) as sulfite ions and reacted with N-(9-acridinyl)maleimide (NAM), which was used as a fluorescent reagent. The fluorescence of NAM-sulfite in micro-fluidic channel was detected. The calibration curve of sulfite ions in the range of 1.5-30 μmol/L (SO₂ 3-60 ppbv) showed a linear relation R² = 0.995, and the relative standard deviation (R.S.D.) was 1.9% for 10 μmol/L sulfite ions in five measurements. The entire measurement procedure was achieved by the integrated microchip, and the consumption of reagents was drastically reduced. It was satisfactory to apply this method to determine on-line the SO₂ level in the air.     

Flammability studies of impregnated paper sheets

Paper sheets impregnated with flame retardants made from agricultural residues and other additives were studied with the cone calorimeter. The use of sugar beet ethanol eluent (SBE), CaCl₂, and ZnCl₂ lowered the peak rate of heat release (PRHR) the most in comparison to water treated material. The average effective heat of combustion (AEHC) was lowered by most of our treatments with the exception of BMIC (butylmethylimidazolium chloride)/starch (BMS). The average mass loss rate was lowered by all the treatments, but the most by the use of ZnCl₂ and CaCl₂ treatments. Mass losses were the least with SBE, CaCl₂/NaOH/starch, and CaCl₂/NaOH treatments. The BMS sample exhibited the greatest total heat release while SBE samples gave the smallest value of the parameter. The flame retarding effect of SBE was ascribed to the presence of ferulates which prevented the formation of volatile products by condensing into polycyclic aromatic residue.     

Studies on photochemical reactions of air pollutants. XIV.Photooxidation of sulfur dioxide in air by various air pollutants

Upon exposure to sunlight, or to artificial light at wavelengths longer than 290 nm, sulfur dioxide in air underwent oxidation to give sulfur trioxide in the presence of air pollutants such as biacetyl (2,3-butanedione), benzaldehyde and nitrogen dioxide, but not in their absence. Only nitrogen dioxide completely oxidized sulfur dioxide to sulfur trioxide.     

Optosensing of hydrogen sulphide through paper impregnated with lead acetate

Summary A flow-through optosensing method for hydrogen sulphide analysis is described, which involves reflectance measurements through optical fibres on paper impregnated with lead acetate. Levels as low as 50 ppb H₂S could be measured with high reproducibility within 10 s. The response was affected by flow rate and relative humidity, both of which were controlled during the measurement process. The method provides a sensitive real-time analysis of hydrogen sulphide and could be carried out remote from the instrumentation system.

---

Schwefelwasserstoffbestimmung durch Bleiacetat-imprägniertes Papier mit Hilfe eines optischen Sensors

     

The adsorption properties of organic sulfur compounds on zeolite-based sorbents impregnated with rare-earth metals

Dimethyl disulfide (DMDS) and dimethyl sulfide (DMS) are non-polar, stable, organic sulfur compounds found in liquefied petroleum gas, and their oxidation in the atmosphere results in the formation of tropospheric sulfur dioxide, which is subsequently converted into sulfuric acid, as the main factor of acid rain. In the present study, adsorption processes were devised based on the use of modified zeolite impregnated with rare-earth metals (Ce, La or Pr) for the adsorption of DMDS and DMS, and their sorption capacities were compared with that of commercial zeolite [Zeolite-Y, Ultra Stable Y(USY)]. The adsorption capacities of adsorbents were tested using a micro liquid flow reactor at room temperature. USY impregnated with cerium oxide (UC-10) had excellent DMDS and DMS adsorption capacities as compared with the other adsorbents tested. It was found that impregnation of USY with rare-earth metal such as Ce improved the sulfur adsorption capacity of zeolite. The form of the Ce promoter impregnated into USY was determined by FT-Raman spectroscopy. Adsorbents were characterized by X-ray fluorescence spectrometer, X-ray diffraction, and BET and the results obtained are discussed.     

Modification of Amaya-Sugiura passive sampling spectrophotometric method of nitrogen dioxide determination in ambient air

Summary On the example of the previously tested method of nitrogen dioxide determination in ambient air two aspects of wind influence on the badge-type sampler performance were discussed: an appropriate design of the sampler eliminating any open recess over the face of the sampler and so called starvation effect i.e. decrease in the mass of analyte absorbed by the sampler at wind velocities below 20 cm/s. The wind effect on the performance of the passive sampler has been diminished from about 150% to maximum 20%.     

Novel multi-sorbent for sampling and determination of trace volatile organic sulfur compounds in ambient air

Novel adsorbent APSG-MW (average particle size 215?µm and specific surface 98 m²?g^?1) bonding multi-walled carbon nanotubes (MWCNTs) on silica gel are obtained. Then the sampling tubes filled with Tenax TA and APSG-MW are prepared and the adsorptive capacity of Tenax TA/APSG-MW for volatile organic sulfur compounds (VOSCs) is studied. The data show that the adsorption and desorption recoveries of multi-sorbent for VOSCs are satisfactory (>85%), and the breakthrough values are large (>16?L?g^?1) enough to absorb VOSCs in ambient air. The sampling precision of the sorbent tubes meets TO-17 criteria. The sampling tubes are successfully used to concentrate and analyze a sample of landfill air, and the major S compounds are identified.