涂布2,4-二硝基苯肼的环形溶蚀器/滤膜系统和高效液相色谱法检测大气中二羰基化合物

建立了环形溶蚀器/滤膜系统(Annular denuder/filter pack system)和2,4-二硝基苯肼(DNPH)-高效液相色谱法(HPLC)采集和检测大气中气相和颗粒相二羰基化合物的方法。DNPH作为吸附剂分别涂布在环形溶蚀器的内壁和3层滤膜上,当大气样品经过环形溶蚀器时,含有气相二羰基化合物的气体吸附到环形溶蚀管内壁上与DN-PH发生反应,而颗粒相部分穿过环形溶蚀管,采集到滤膜上。样品经乙腈洗脱、浓缩后,采用HPLC进行分析。根据不同的采样流速、采样时间和DNPH的涂布量采集到的二羰基化合物的浓度,确定的最佳采样条件为:采样流速4 L/min,采样时间4~5 h,DNPH浓度0.47 g/L。使用Tedlar bag验证环形溶蚀器乙二醛和甲基乙二醛的采集效率(分别为82%和85%)。利用此方法对实际大气中的二羰基化合物进行了检测。     

Gas collection efficiency of annular denuders: A spreadsheet-based calculator

Denuders are widely used for atmospheric analysis. Annular denuders are especially well-suited for preconcentration of trace gases compared to simpler single tube designs. While traditionally coated annular denuders have both bounding surfaces that behave as sinks, annular denuders/membrane-based scrubbers with the same basic geometric design and with only one of the annular surfaces functioning as sink (e.g., a membrane tube whose outer surface behaves as a sink disposed within an inert jacket tube) have become common. However, the gas collection efficiency of such devices cannot be expressed as a simple equation with fixed constants and there is no presently available tool to a priori determine the denuder performance or to design denuders with specific removal efficiencies at specific sampling rates. This paper presents a simple to use “spreadsheet calculator” for concentric annular denuders of any dimension based on known solutions to analogous heat transfer problems. The results from the present spreadsheet calculator are compared with results from a commercial computational fluid dynamics package (Fluent™; this takes significant expertise and development effort to run)—the two approaches produce essentially the same results. The present spreadsheet calculator can be used easily and simply without training and will be a useful tool for denuder users and designers.     

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.     

Annular diffusion denuder for simultaneous removal of gaseous organic compounds and air oxidants during sampling of carbonaceous aerosols

A specially designed annular diffusion denuder for simultaneous removal of organic gaseous compounds and atmospheric oxidants in carbonaceous aerosol sampling is presented. Various kinds of denuder coatings were compared with respect to the collection efficiency of both organic gaseous compounds and NO₂ and ozone. The optimum sorbent is a mixture of activated charcoal and sulfite on molecular sieve. To ensure high collection efficiency over long-term field operation, two annular diffusion denuders are combined in series. The first half of the first denuder is filled with Na₂SO₃ on molecular sieve (23 cm long layer) while the second half of the first denuder and the whole second denuder are filled with activated charcoal (the total length of the charcoal section is 67 cm).     

Sampling and determination of gas phase divalent mercury in the air using a KCl coated denuder

KCl coated denuders were employed for the measurement of divalent mercury (Hg²⁺) species in the air. Laboratory tests show that gaseous Hg²⁺ can be collected by the denuder with an average efficiency of 98% and elemental Hg will pass through it freely. Hg²⁺ trapped in the denuder can be quantitatively extracted by 1 mol/L HCl and analyzed by the method of SnCl₂ reduction-CVAFS determination. Hg²⁺ concentrations of 0.04–0.15 ng m^–3 corresponding to about 2–9% of the total gaseous mercury in the ambient air were determined at several sampling locations. Received: 24 September 1996 / Revised: 14 January 1997 / Accepted: 18 January 1997     

Evaluation and applications of a gaseous mercuric chloride source

In this study, a diffusion-type device for generating gaseous mercuric chloride (HgCl₂) was systematically evaluated and applied to validate the annular denuder method for sampling gaseous HgCl₂ species in a synthetic gas stream. The results show that it takes at least 48 h for the system to reach a steady-state condition after the diffusion cell reaches the temperature set-point and the carrier gas is activated. The primary Hg species from the source was proven to be HgCl₂. In the temperature range from –5.00 to 11.80 °C, the Hg emission rates from the source vary from 1.8 to 14.2 pg min^–1. It is shown that, under the experimental conditions examined, KCl-coated annular quartz denuders designed for ambient reactive gaseous mercury (RGM) collection could quantitatively collect HgCl₂. It is also demonstrated that the impactors used to remove coarse airborne particulate matter could lead to a loss of up to one third of the HgCl₂ in the gas stream.     

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     

Sampling and determination of gas phase divalent mercury in the air using a KCl coated denuder

KCl coated denuders were employed for the measurement of divalent mercury (Hg²⁺) species in the air. Laboratory tests show that gaseous Hg²⁺ can be collected by the denuder with an average efficiency of 98% and elemental Hg will pass through it freely. Hg²⁺ trapped in the denuder can be quantitatively extracted by 1 mol/L HCl and analyzed by the method of SnCl₂ reduction-CVAFS determination. Hg²⁺ concentrations of 0.04–0.15 ng m^–3 corresponding to about 2–9% of the total gaseous mercury in the ambient air were determined at several sampling locations.     

Condenser-type diffusion denuders for the collection of sulfur dioxide in a cleanroom

High-efficiency condenser-type diffusion denuders of cylindrical and planar geometries are described. The film condensation of water vapor onto a cooled denuder surface can be used as a method for collecting water-soluble gases. By using SO(2) as the test gas, the planar design offers quantitative collection efficiency at air sampling rates up to 5 L min(-1). Coupled to ion chromatography, the limit of detection (LOD) for SO(2) is 0.014 ppbv with a 30-min successive analysis sequence. The method has been successfully applied to the analysis of temperature- and humidity-controlled cleanroom air.     

Prediction of gas collection efficiency and particle collection artifact for atmospheric semivolatile organic compounds in multicapillary denuders

A modeling approach is presented to predict the sorptive sampling collection efficiency of gaseous semivolatile organic compounds (SOCs) and the artifact caused by collection of particle-associated SOCs in multicapillary diffusion denuders containing polydimethylsiloxane (PDMS) stationary phase. Approaches are presented to estimate the equilibrium PDMS–gas partition coefficient (K_pdms) from a solvation parameter model for any compound, and, for nonpolar compounds, from the octanol–air partition coefficient (K_oa) if measured K_pdms values are not available. These estimated K_pdms values are compared with K_pdms measured by gas chromatography. Breakthrough fraction was measured for SOCs collected from ambient air using high-flow (300 L min⁻¹) and low-flow (13 L min⁻¹) denuders under a range of sampling conditions (−10 to 25 °C; 11–100% relative humidity). Measured breakthrough fraction agreed with predictions based on frontal chromatography theory using K_pdms and equations of Golay, Lövkvist and Jönsson within measurement precision. Analytes included hexachlorobenzene, 144 polychlorinated biphenyl congeners, and polybrominated diphenyl ethers 47 and 99. Atmospheric particle transmission efficiency was measured for the high-flow denuder (0.037–6.3 μm diameter), and low-flow denuder (0.015–3.1 μm diameter). Particle transmission predicted using equations of Gormley and Kennedy, Pich, and a modified filter model, agreed within measurement precision (high-flow denuder) or were slightly greater than (low-flow denuder) measured particle transmission. As an example application of the model, breakthrough volume and particle collection artifact for the two denuder designs were predicted as a function of K_oa for nonpolar SOCs. The modeling approach is a necessary tool for the design and use of denuders for sorptive sampling with PDMS stationary phase.     

Light collection enhancement of the digital x-ray detector using Gd2O2S:Tb and CsI:Tl phosphors in the aspect of nano-scale light dispersions

The nano-scopic light collection is investigated for the Active Matrix Flat-Panel Imagers (AMFPIs). The simulations using two kinds of screens are shown for light collection of x-rays. Enhancement of the light collection is accomplished by the microlens system incorporated with x-ray detector. For digital radiographic and mammographic applications, indirect detection imagers use Gd₂O₂S:Tb or CsI:Tl scintillation screens to convert the x-ray into visible photons. The light collection efficiencies for Gd₂O₂S and CsI are obtained. In Gd₂O₂S, the 27 kVp and 82 μm are the highest light collection cases in both Lambertian and Isotropic geometries. In CsI, 20 keV and 150 μm case have the highest light collection efficiency. So, x-ray energy and scintillator thicknesses are considered as the optimized light collection. The optimum thickness and x-ray energy combination are used for the detector of this study. In this paper, it is concluded that the screens between 17 kVp and 25 kVp have higher light collections, which could be considered as the clinical purposes if it is necessary. This energy range is compared with other energy cases, which are examined in the study.     

Speciation of volatile mercury species present in digester and deposit gases

Volatile mercury compounds have been speciated in gases evolved from fermentation of sewage sludge as well as municipal waste. The species were trapped by sequential sampling, using a noble‐metal trap in series with an activated‐carbon trap. Thermally desorbed Hg⁰ and (CH₃)₂Hg were separated by GC at 70 °C and detected by cold vapour atomic fluorescence spectroscopy after thermal reduction. The amounts of mercury detected in the sewage gas correspond to concentrations in the range 50–110 ng m⁻³ for both species whereas the deposit gases were found to contain only elemental mercury. Monomethylmercury species could not be positively identified in any of the gas samples. Copyright © 1999 John Wiley & Sons, Ltd.     

Penetration of nanoparticles through screen-type diffusion batteries

The deposition of aerosol nanoparticles from Stokes flows in screen-type diffusion batteries designed for the determination of diffusion coefficients for suspended nanoparticles is considered. Average fiber collection efficiencies η calculated for screens consisting of two perpendicularly contacting rows of parallel equidistant straight fibers agree with the experimental data obtained for woven screens within the Peclet number range Pe = 0.15−1000. It is shown that, for dense screens, the η ∼ Pe^−2/3 power dependence is valid at Pe > 10. For rarefied screens, this dependence is fulfilled down to Pe ∼ 0.1. At Pe ≪ 1, the integral flow of particles advancing on the fibers of the first row in the screen and the fiber collection efficiency, η of an isolated row tends to a geometrical limit, which is equal to the ratio of the distance between the axes of the fibers to the fiber diameter.     

Determination of chlorinated hydrocarbons in single and multi component test gases

Summary For comparing the efficiency of active and diffusive sampling methods two diffusive samplers with different properties were used to determine chlorinated hydrocarbons (CH₂Cl₂, CHCl₃, CCl₄) in single and multi component test gas mixtures. One of the chosen diffusive samplers can also be used for active sampling.In general, good correlations of all tested methods could be observed in the direct comparison of active and diffusive sampling and in the determination of the efficiencies.During the application of active and diffusive sampling methods in multi component test gases of the analytes possible interferences could not be ascertained.     

Determination of aromatic hydrocarbons in air using diffusion denuders

The results of a study to evaluate a recently developed denuder sampling system for the determination of aromatic hydrocarbons in air are presented. Denuders of different lengths were tested in laboratory experiments by means of dynamically generated test gases at conditions similar to those at workplaces. Uptake rates, adsorption capacities as well as desorption efficiencies were measured at different sampling parameters. The influence of air humidity on the adsorption behaviour was determined. Finally, the suitability of the system for outdoor air investigations was checked. The denuders were very suitable for the determination of aromatic hydrocarbons in workplace air; the general feasibility to investigate outdoor air samples was demonstrated.     

High-volume sampling of airborne polychlorobiphenyls with amberlite xad-2 resin

Polyurethane foam, polyurethane foam coated with DC-200, Florisil, and Amberlite XAD-2 resin have been evaluated in a small-scale comparative study of their ability to sample airborne polychlorobiphenyls. XAD-2 resin has an excellent collection efficiency for tetrachlorobiphenyl at 1 l min^-1 flow rates and is also suitable for high-volume air sampling. A high-volume air sampler was modified to sample both particulate and vapor-phase polychlorobiphenyls by incorporating the XAD-2 resin behind a glass fiber filter. When the sampling system was operated at a flow rate of 0.7 m³ min^-1 for 24 h, the collection efficiencies for tetrachlorobiphenyl and Aroclor 1221 were 96.5% and 83.0%, respectively.     

Improved determination of gaseous divalent mercury in ambient air using KCl coated denuders

An improved method for the determination of gaseous divalent mercury (GDM) in ambient air using KCl coated denuders has been developed and tested. GDM collected in the KCl coated denuders can be quantitatively desorbed at 450?°C in 10 min. After being complete thermally reduced to Hg⁰ at 900?°C, all mercury released from the denuder is pre-concentrated on the analytical Au trap, and detected by cold vapor atomic fluorescence spectrometry (CVAFS). The absolute detection limit of the method is less than 3 pg. Preliminary data of GDM concentration in ambient air from different sampling stations show that GDM concentrations in the urban air of Göteborg are much higher than in rural air (Rörvik and Sasetta), which indicates the anthropogenic origin of GDM.     

Direct thermal desorption of semivolatile organic compounds from diffusion denuders and gas chromatographic analysis for trace concentration measurement

A novel method for collection and analysis of vapor-phase semivolatile organic compounds (SOCs) in ambient air is presented. The method utilizes thermal desorption of SOCs trapped in diffusion denuders coupled with cryogenic preconcentration on Tenax-TA and analysis by high resolution gas chromatography (GC)-electron-capture detection (ECD). The sampling and analysis methods employ custom-fabricated multicapillary diffusion denuders, a hot gas spike (HGS) apparatus to load known quantities of thermally stable standards into diffusion denuders prior to sample collection, a custom-fabricated oven to thermally desorb SOCs from the diffusion denuder, and a programmable temperature vaporization (PTV) inlet containing a liner packed with Tenax-TA for effective preconcentration of the analytes and water management. High flow rates into the PTV inlet of 750mLmin(-1)during thermal desorption are ca. a factor of ten greater than typically used. To improve resolution and retention time stability, the thermal desorption and PTV inlet programming procedure includes three steps to prevent water from entering the analytic column while effectively transferring the analytes into the GC system. The instrumentation and procedures provide virtually complete and consistent transfer of analytes collected from ambient air into the GC evidenced by recovery of seven replicates of four internal standards of 90.7+/-4.0-120+/-23% (mean+/-95% confidence interval, CI). Retention time based compound identification is facilitated by low retention time variability with an average 95% CI of 0.024min for sixteen replicates of eight standards. Procedure details and performance metrics as well as ambient sampling results are presented.     

Simultaneous measurements of formaldehyde and ozone in air by annular denuder-HPLC techniques

Summary A denuder sampling method combined with HPLC analysis for the simultaneous determination of formaldehyde and ozone in ambient air is described. It is based on the reactions of CH₂O and O₃ with 2,4-dinitrophenylhydrazine (DNPH) and 4-allyl-2-methoxyphenol (eugenol)_respectively, both acting as coatings of two annular denuders connected in series. Formaldehyde released from the ozonolysis of eugenol is quantitatively collected on a third downstream DNPH-coated denuder. The two DNPH denuders are then extracted and analyzed as hydrazone derivative by HPLC with UV absorbance detection.The stoichiometric factor of the eugenol-ozone reaction was found to be 2.0±0.1 moles of O₃ per mole of CH₂O. The limits of detection are 0.8gm^–3 CH₂O and 3gm^–3 O₃ for 100l air sampled, corresponding to 1-h sampling at 1.7l min^–1.     

Determination of low boiling aldehydes in air and exhaust gases by using annular denuders combined with HPLC techniques

Summary An improved procedure for the HPLC determination of C₁–C₃ aldehydes in environmental samples is described. These air pollutants are quantitatively collected on annular denuders coated with 2,4-Dinitrophenylhydrazine and analyzed as hydrazone derivatives by HPLC with UV absorbance and voltammetric detection. Collection efficiencies of aldehydes are reported and compared with other available methods. Practical examples of the application of the method are given.This work has been part of the Dottorato di Ricerca program carried out at the University of Rome.Dedicated to Prof. Dr. A. Liberti on the occasion of his 70th birthday.