Comparative study of the adsorption performance of a multi-sorbent bed (Carbotrap, Carbopack X, Carboxen 569) and a Tenax TA adsorbent tube for the analysis of volatile organic compounds (VOCs)

A comparison between two types of adsorbent tubes, the commonly used Tenax TA and a multi-sorbent bed (Carbotrap, Carbopack X, Carboxen 569) tube developed in our laboratory, has been done to evaluate their usefulness in the analysis of VOCs in ambient air. Duplicate indoor and outdoor samples of Tenax TA and multi-sorbent tubes of 10, 20, 40, 60 and 90 l were taken in Barcelona city (Spain) on July and October of 2009. Breakthrough values (defined as %VOCs found in the back tube) were determined for all sampling volumes connecting two sampling tubes in series. The analysis was performed by automatic thermal desorption (ATD) coupled with capillary gas chromatography (GC)/mass spectrometry detector (MSD). Significant differences between the concentrations obtained-from multi-sorbent bed and Tenax TA tubes are observed for the very volatile compounds (56 °C < boiling point < 100 °C and 4 kPa < vapour pressure (20 °C) < 47 kPa) (e.g. acetone, isopropanol, n-hexane) and for alcohols and chlorinated compounds (e.g. 1-butanol, carbon disulphide, dichloromethane, chloroform, carbon tetrachloride, trichloroethylene, tetrachloroethylene), being the concentrations found higher in multi-sorbent bed than in Tenax TA tubes. On the other hand, mainly all compounds with boiling points higher than 100 °C (except α-pinene, chlorinated and polar compounds) do not show significant differences between the obtained multi-sorbent bed and Tenax TA tube concentrations. For the concentrations obtained (5 ppt to 100 ppb), Tenax TA present high breakthrough values (from 0 to 77%) for mainly all compounds and sampling volumes studied. On the other hand, multi-sorbent bed tubes do not exhibit important breakthrough values for these compounds, except the VVOCs ethanol (for all sampled volumes), and acetone, dichloromethane and isopropanol (for sampling volumes over 40 l). The concentration differences observed between Tenax TA and multi-sorbent bed tubes are directly related to the high breakthrough values determined for Tenax TA adsorbent.     

The stability of Tenax TA thermal desorption tubes in simulated field conditions on the HAPSITE® ER

Due to the growing need to monitor aircraft cabin, cockpit and breathing-line air quality, functional assessment of sampling equipment for the specialised field conditions of flight need to be established for both in-flight and ground safety. In this article, we assess the reliability of Tenax TA thermal desorption tubes to perform under various relevant field sampling conditions, such as storage temperature, loading temperature, vibrational velocity, gravitational force (G Force) and altitude pressure with semi-real-time gas chromatograph-mass spectrometer (GC-MS) analysis on the field portable HAPSITE^® ER (Hazardous Air Pollutants on Site Extended Range) instrument. First, we show that Tenax TA thermal desorption tubes can handle storage under extreme environmental conditions, 4–77°C, over numerous analytical test cycles. Next, we confirm that extreme loading temperature, both hot (77°C) and cold (4°C), does not affect the analytical reliability of Tenax TA thermal desorption tubes. Then, we illustrate that G Force may have a significant (p ≤ 0.0364) effect on Tenax TA performance while vibrational velocity (p ≤ 0.7265) and low ambient air pressure (p ≤ 0.1753), such as that found at high altitude, do not. Finally, several Tenax TA thermal desorption tubes were flight-tested, demonstrating that the durability of these tubes maybe insufficient for use on military cargo aircraft (p = 0.0107). The results presented here provide a rationale for additional testing of Tenax TA thermal desorption tubes for flight suitability.     

Development of a method for the monitoring of odor‐causing compounds in atmospheres surrounding wastewater treatment plants

This study describes the development of an analytical method based on active collection in a multisorbent Tenax TA/Carbograph 1TD tube, followed by thermal desorption and GC‐MS for the determination of 16 volatile organic compounds in air samples. The analyzed compounds include ozone precursors and odor‐causing compounds belonging to different chemical families (sulfur‐ and nitrogen‐containing compounds, aldehydes, and terpenes). Two types of sorbents were tested and desorption conditions (temperature, time, and sampling, and desorption flow) were evaluated. External calibration was carried out using the multisorbent bed. Method detection limits in the range 0.2–2.0 μg m^?3 for 1 L samples were obtained. The method was applied for determining the target compounds in air samples from two different wastewater treatment plants. Most compounds were detected and toluene, limonene, and nonanal were found in particularly high concentrations with maximum values of 438, 233, and 382 μg m^?3, respectively.     

Determination of volatile organic compounds in industrial wastewater plant air emissions by multi-sorbent adsorption and thermal desorption-gas chromatography-mass spectrometry

This paper describes the process of determining the presence of volatile organic compounds in air emissions from industrial wastewater treatment plants (WWTP). The analytical method, based on thermal desorption-gas chromatography-mass spectrometry, was developed to simultaneously determine of 99 volatile organic compounds (VOCs) in air samples. This method is rapid, environmentally-friendly (since no organic solvents are used to extract the analytes) and compatible with a large range of thermally stable polar and apolar compounds. The target VOCs were selected on the basis of their occurrence in real samples and their adverse effects on the environment and human health. To cover the wide range of target compounds, multisorbent tubes filled with Tenax TA and Carbograph 1TD were used. Method validation showed good repeatabilities, low detection limits, a high linear range and good recoveries. At a fixed sample volume of 600?mL no significant losses for any of the target compounds were found in the samples. Stability during storage indicated that samples must be keep refrigerated at 4°C and analysed within three days of collection. Real samples were taken from air emissions of an industrial wastewater treatment plant located in the Southern Industrial Area of Tarragona (Spain) with the aim of studying its contribution as a source of atmospheric VOCs. This WWTP collects wastewater from several chemical factories which produce isocyanates, polyurethanes, chlorinated organics and functional chemicals among other products. Samples from the collecting tank after the primary sedimentation showed higher VOC concentrations than samples from the secondary treatment tank. The most abundant VOCs found in these emissions are included in the USEPA List of Hazardous Air Pollutants. The highest values correspond to acrylonitrile (up to 1843?µg?m^?3) and styrene (up to 573.70?µg?m^?3). The levels of chloroform, 1,4-dioxane, ethylbenzene, 1,2,3-trimethylbenzene and 1,4-diethylbenzene were also high.     

Measurements Of Biogenic Hydrocarbons And Their Atmospheric Degradation In Forests

Abstract

An analytical procedure for the sampling and quantitative determination of biogenic hydrocarbons in the atmosphere is presented. The method is based on the adsorptive preconcentration of the hydrocarbons using Tenax TA/Carbopack B filled sampling tubes followed by thermodesorption of the trapped compounds and gas chromatographic analysis. To avoid losses of the biogenic alkenes as a consequence of their reaction with ozone on the adsorbents during the sampling step, an ozone scrubber is used in front of the adsorption tubes. Diurnal variations of the monoterpene- and ozone-concentrations are determined at different heights in and above a forest stand (coniferous and deciduous trees) in the Vosges (Col du Donon, 760 m a.s.l.) in order to elucidate the importance of terpene-oxidation reactions on the formation of peroxidic products in forest air.     

Novel adsorbent based on multi-walled carbon nanotubes bonding on the external surface of porous silica gel particulates for trapping volatile organic compounds

A novel adsorbent, 3-amino-propylsilica gel-multi-walled carbon nanotubes (APSG-MW), was prepared by chemical bonding multi-walled carbon nanotubes on silica gel. The surface area of APSG-MW was 98 m²/g, and the particle size was between 60 and 80 mesh with the average size of 215.0 μm. The adsorption capability of the new adsorbent to volatile organic compounds (VOCs) was measured. The effect of water to the adsorbent and its stability during storage were also investigated. Duplicate precision (DP) and distributed volume pair (DVP) on the basis of the EPA TO-17 criteria were estimated. The results showed that the sampling precision of the adsorbent was more superior compared to the MWCNTs because of the better air permeability. The new adsorbent was successfully applied in the determination of VOCs in ambient indoor air.     

A simple and fast micromethod for the analysis of polychlorinated biphenyls in air by sorbent enrichment and ultrasound-assisted solvent extraction

A combination of sorbent enrichment and ultrasound-assisted solvent extraction has been used to determine polychlorinated biphenyls in air. Analytes were sampled by pumping a known volume of air through a porous polymer (Tenax TA). The enriched adsorbent was transferred into a glass vial, and ultrasound-assisted extraction of the analytes was then performed in n-hexane. Quantification was carried out by using gas chromatography coupled to tandem mass spectrometry. Breakthrough volume of the sampling step was studied, indicating that 10 m³ of air could be processed without losses of the most volatile compounds. Good recoveries (75–96%) were obtained, and limits of detection at the sub ng m^–3 were achieved for all the analytes. The proposed method is very simple and fast, avoiding the use of large solvent volumes and time-consuming preconcentration steps.     

Application of thermal desorption to the development of a gas chromatographic/mass spectrometric method for the determination of toluene,chlorinated aromatic hydrocarbons,and 2,3,7,8-tetrachlorodibenzo-p-dioxin in combustion emissions

A fast and accurate analytical method, which uses commercially available adsorbents (Tenax TA, Carbotrap B and C, and Carbosieve S-III), was developed for the sampling and determination of aromatic hydrocarbons, chloroaromatic compounds, and 2,3,7,8-tetrachlorodibenzo-p-dioxin. The breakthrough volume data show that Carbotrap C has a good capacity for compounds of high molecular weight, whereas Carbosieve S-III and Tenax TA are efficient for volatile compounds. The organic components are thermally desorbed and transferred to a gas chromatograph/mass spectrometer. Importantly, thermal desorption avoids conventional solvent extraction procedures and also allows reuse of adsorbent tubes. Preliminary results for recovery of analytes from tubes packed with single adsorbent prove that a single-adsorbent bed is not capable of sampling a wide range of compounds. The best method to obtain the desired collection and desorption properties is to use adsorbent tubes containing several different materials. The results of optimization studies are summarized.     

Thermal desorption—gas chromatography for the determination of benzene, aniline, nitrobenzene and chlorobenzene in workplace air

Sampling on Tenax TA of different mesh sizes followed by thermal desorption and gas chromatography was evaluated as a simple method for the determination of benzene, aniline, nitrobenzene and chlorobenzene in the workplace air. An alternative sampling technique in place of pump sampling was developed. Quantitative recoveries were obtained in the mass range 0.04–10 μg. It was found that air humidity had no effect on recovery. The charged tubes can be stored at room temperature for 5 days with no change in recovery. The particle size of Tenax TA has no significant effect on adsorption and desorption.     

Volatile organic compounds in an urban environment: a comparison among Belgium,Vietnam and Ethiopia

The effects of urban and indoor air pollution on human health are a major environmental concern for all, but not much has been researched in the developing world. Specifically, quantitative data on the occurrence of volatile organic compounds (VOCs) – main contributors to air pollution – in Asia and Africa are scarce compared to the availability of data in the developed world. This paper presents one of the first studies focusing on the analysis and occurrence of VOCs in Vietnam and Ethiopia, which constitutes part of the novelty of this work. A spectrum of 34 VOCs was measured at eight different urban sites in Ghent (Belgium), Hanoi (Vietnam), Jimma and Addis Ababa (Ethiopia) during three sampling campaigns from September 2008 to September 2010. Sampling was done in an active way by means of sorbent tubes filled with Tenax TA. The analysis was done by TD-GC-MS using internal standard calibration. Data were interpreted and compared in terms of (i) individual, subgroup and total VOCs concentration (TVOCs), (ii) indoor-to-outdoor (I/O) concentration ratios, (iii) source identification by diagnostic ratio and/or correlation coefficients, and (iv) ozone formation potential (OFP) at outdoor sites based on up-to-date maximum incremental reactivity (MIR). I/O concentration ratios varied between 0.2 and 30, with big differences noticed with respect to the type of VOC(s) considered and the type of outdoor sampling location. The highest TVOC concentrations were measured in street samples with maximum values of 54?µg/m³ in Ghent, 507?µg/m³ in Hanoi and 318?µg/m³ in Addis Ababa illustrating the large difference in ambient air quality levels. This is also reflected in the arithmetic mean OFP values (µg/m³) of 82, 1308 and 596 in Ghent, Hanoi and Addis Ababa, respectively. Results of this study could be helpful to support formulation of national policy with regard to ambient air quality.     

Application of the molecularly imprinted solid-phase extraction to the organophosphate residues determination in strawberries

This study describe an analytical method employing gas chromatography (GC) using flame photometric detection that has been developed for the simultaneous determination of organophosphate pesticides (diazinon, disulfoton, parathion, chlorpyrifos and malathion) in strawberry samples. For this purpose, molecularly imprinted solid-phase extraction was applied as a sample preparation technique. The method was linear in the ranges from 0.10 to 1.00?μg?g^?1, for diazinon, disulfoton, parathion and chlorpyrifos, and 0.10 to 2.00?μg?g^?1 for malathion with r?>?0.99. The detection limits (LD) ranged from 0.02 to 0.05?μg?g^?1. Recovery studies yielded average recoveries in the range of 65.25 to 87.70?%. These results showed the potential of this technique for organophosphate residue monitoring in strawberry samples.     

Volatile organic compounds in landfill odorant emissions on the island of Mallorca

This study provides data on the occurrence of volatile organic compounds (VOCs) in the biogas emission from a landfill located on the island of Mallorca (Balearic Islands, Spain), where 200,000 tonnes of urban solid wastes are dumped every year. Three different sampling cells, of differing waste ageing were investigated in August 2008, during the main tourist season and the warmest possible weather conditions. Samples were collected in Nalophan? bags according to the standard European method EN 13725 followed by VOCs adsorption onto Carboxen 1000? and Tenax TA? materials prior to thermal desorption and analysis by GC-MS. In total 42 VOCs were analysed, using external standards, out of which 36 were positively identified. Detected VOCs in µg?m^?3 were alkanes (19–62), aldehydes (65–98), ketones (78–129), alcohols (67–78), esters (25–33), BTEX (83–106), halogenated compounds (16–39), terpens (1.4–2.4) and reduced sulphur compounds (2.6–4.2), showing different concentrations on each one of the three cells. Emitted VOCs showed some similarities with other previous studies from China and Turkey, while large differences to an Italian study. The benzene-to-toluene ratio (B:T) showed values in the range of 0.13 to 0.20 characteristic of biogas. H₂S and NH₃ gases emitted by the landfill were measured in-situ utilising Dräger? Tubes for Short-Term-Measurements, showing concentration levels of ≤800?µg?m^?3 and <300?µg?m^?3, respectively, which is higher than the determined VOCs in accordance with previous studies. Samples were examined with dynamic olfactometry following standard European method EN 13725, to determine a potential statistical linear correlation between odour and VOC concentrations. Such correlations were not observed probably owing to the large number of compounds emitted from garbage which are not quantified, yet causing positive results in olfactometry.     

Determination of beer aroma compounds using headspace solid-phase microcolumn extraction

A rapid sampling technique for the analysis of beer aroma compounds is described. The headspace (10 ml) is passed through the microcolumn filled with 5 mg of Tenax TA and thermally desorbed in a modified GC inlet (modification is described). Eight compounds (from acetaldehyde to 2-phenylethanol) in four beer samples were analyzed. The correlation coefficients (r²), repeatability (RSD) and limits of detection (LOD) were 0.9973-0.9994, 2.1-6.9% and 0.00002-0.13 mg/l, respectively. The methodology can be useful for routine beer sample analysis.     

Development of a thermal desorption-gas chromatography–mass spectrometry method for determining personal care products in air

This study describes the development of a new analytical method for determining 14 personal care products (PCPs) – nine synthetic musks, four parabens and one insect repellent – in air samples. The method is based on active sampling on sorbent tubes and thermal desorption-gas chromatography–mass spectrometry analysis, and is rapid, sensitive and drastically reduces the risk of sample contamination. Three kinds of tubes and traps were tested, those filled with Tenax TA being the most suitable for this study. Method validation showed good repeatability and reproducibility, low detection limits (between 0.03 ng m⁻³ for DPMI and 12.5 ng m⁻³ for propyl paraben) and good linearity for all compounds. Stability during storage indicated that samples must be kept refrigerated at 4 °C and analysed within 1 week of collection. The applicability of the technique to real samples was tested in different indoor and outdoor atmospheres. The total PCP values for indoor air ranged from 135 ng m⁻³ in a pharmacy to 2838 ng m⁻³ in a hairdresser's, whereas the values for outdoor air ranged from 14 ng m⁻³ for a suburban environment to 26 ng m⁻³ for an urban environment. In general, the most abundant synthetic musks were galaxolide (5.9–1256 ng m⁻³), musk xylene (1.6–766 ng m⁻³) and tonalide (1.1–138 ng m⁻³). Methyl and ethyl paraben (2.4–313 ng m⁻³ and 1.8–117 ng m⁻³, respectively) were the most abundant parabens. Although thermal desorption methods have been widely used for determining volatile organic compounds, they are rarely used with semi-volatile compounds. This study thus demonstrates that the thermal desorption method performs well with semi-volatile compounds and, for the first time, that it can be used for determining PCPs.     

Multi-layer cartridges filled with multi-walled carbon nanotubes for the determination of volatile organic compounds in indoor air.

A kind of new multi-layer adsorbent including Tenax TA/multi-walled carbon nanotubes (MWCNTs)/Carboxen 564 was developed for collecting volatile organic compounds. The adsorption and desorption efficiencies of 11 kinds of adsorbents (including Activated charcoal, Tenax TA, Carboxen 564, Chromosorb 101, Chromosorb 102, Chromosorb 103, Chromosorb 105, Porapak Q, GDX 301, XAD-2, and MWCNTs) were compared. By combining the advantages of Tenax TA, MWCNTs, and Carboxen 564, new type of multi-layer adsorbents was developed. The adsorption and desorption efficiency, the sampling reproducibility, and the effect of water were improved using multi-layer adsorbents, Tenax TA/MWCNTs/Carboxen 564. New multi-layer adsorbents were successfully applied to the determination of volatile organic compounds (VOCs) in ambient air.     

GC-MS Analysis of Organic Vapours Emitted from Polyurethane Foam Insulation

Abstract

The vapours emitted by rigid polyurethane foam at 40° and 80° in dry and in humid (90% RH) air were trapped with a Tenax TA sampling tube and, after thermal desorption, analyzed by high resolution gas chromatography – mass spectrometry. The chromatograms obtained demonstrate a certain characteristic pattern. The qualitative composition of the effluent mixture is basically independent of both temperature and humidity of the foam. Over seventy compounds were identified as polyurethane foam off-gases. Among them the most numerous are hydrocarbons. The most abundant is the blowing agent, trichlorofluoromethane. The most interesting are cyclic acetals, aldehydes, cyclic ethers, alcohols, chloroform and chlorobenzene. The headspace concentration of the majority of them is below 10mg/m³, there are, however, several compounds with the concentration exceeding 100mg/m³.     

Performance evaluation of functionalized ordered mesoporous silica for VOCs adsorption by molecular dynamics simulation

Volatile organic compounds (VOCs) are growing pollutants now that cause the serious environmental pollution and threaten human health. The functionalized ordered mesoporous silica (FOMS) has attracted considerable attention in adsorbing VOCs. In this paper, the molecular dynamics simulation was used to simulate the adsorption performance of FOMS on VOCs (acetone, ethyl acetate and toluene). After simulating different pore sizes (2 nm, 3 nm and 4 nm) adsorption performances of ordered mesoporous silica (OMS) on VOCs, OMS with a pore size of 4 nm was selected to further study the influence of functional groups (vinyl, methyl, and phenyl). The following law was obtained: the saturated adsorption capacities of vinyl-functionalized OMS (V-FOMS) to acetone, ethyl acetate and toluene were 3.045 mmol.g^?1, 2.568 mmol.g^?1 and 1.976 mmol.g^?1 respectively; the saturated adsorption capacities of methyl-functionalized OMS (M-FOMS) to acetone, ethyl acetate and toluene were 2.798 mmol.g^?1, 2.312 mmol.g^?1 and 1.698 mmol.g^?1 respectively; the saturated adsorption capacities of phenyl-functionalized OMS (P-FOMS) to acetone, ethyl acetate and toluene were 2.124 mmol.g^?1, 1.941 mmol.g^?1 and 1.539 mmol.g^?1 respectively. These results show that the adsorption ability of FOMS for different adsorbates follows the sequence of acetone > ethyl acetate > toluene. Furthermore, the interaction between functional groups (vinyl, methyl and phenyl) in FOMS and VOCs was explored. It is found that the interaction between different functional groups and adsorbates is different (interaction energy effect). This interaction energy effect promotes FOMS to better adsorb VOCs. This work would provide fundamental understanding and guidance for the development of novel adsorption materials for the adsorption of VOCs.     

23种挥发性有机化合物在3种吸附剂上漏出容量的测定评价

采用吸附热解吸－气相色谱－质谱法对23种挥发性有机化合物Chromosorb 106、Tenax TA、Tenax TG等3种吸附剂上漏出容量进行了测定。根据实验结果确定了不同的化合物应选择不同的吸附剂及相应的采样体积。结果表明,Chromosorb 106可较好地吸附低沸点的挥发性有机化合物,Tenax TA、Tenax TG均可用于沸点较高的挥发笥有机化合物吸附,这对测定大气中的有机化合物含量采样有一定的参考价值。     

The effect of the wind velocity on the uptake rates of various diffusive samplers

This paper examines the results of experiments carried out in an exposure chamber to determine the wind effects on the performance of various diffusive sampler types commonly used for measuring gaseous pollutants in air. The resistance to wind of six diffusive samplers, two Palmes tubes, a badge with diffusion membrane, the EMD sampler and two radial diffusive samplers for different pollutants was compared in a range of velocities from 0 to 300?cm?s^?1. For all diffusive samplers tested, an increase in uptake rate was observed with increased air velocity usually following a logarithmic function. The consequences are an underestimation in the concentration measured by the diffusive samplers for low wind velocities below 30?cm?s^?1 and conversely an overestimation from 60?cm?s^?1. The magnitude of wind effects depends on diffusive sampler type and exceeds an uptake rate variation of ±20% for the axial diffusion tubes and the EMD sampler. With regard to the characteristics of each diffusive sampler, the dependence of uptake rate on wind velocity was analysed and discussed. The radial diffusive samplers for benzene and particularly the ones having a large and thick porous membrane appear to be the most effective design to minimise the influence of air velocity on passive sampling.     

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.