Comparison of Tenax Ta and Carbotrap for sampling and analysis of volatile organic compounds in air

Optimization of volatile organic compounds sampling from dairy cow exhaled breath using polymer-based solid-phase extraction cartridges for gas chromatographic analysis

We explored appropriate technical setups for the detection of volatile organic compounds (VOCs) from exhaled cow breath by comparing six different polymer-based solid-phase extraction (SPE) cartridges currently on the market for gas chromatography/mass spectrometry (GC-MS) screening. Exhaled breath was sampled at a single timepoint from five lactating dairy cows using six different SPE cartridges (Bond Elut ENV (ENV); Chromabond HRX (HRX); Chromabond HRP (HRP); Chromabond HLB (HLB); Chromabond HR-XCW (XCW) and Chromabond HR-XAW (XAW)). The trapped VOCs were analyzed by dynamic headspace vacuum in-tube extraction GC-MS (DHS-V-ITEX-GC-MS). Depending on the SPE cartridge, we detected 1174-1312 VOCs per cartridge. Most VOCs were alkenes, alkanes, esters, ketones, alcohols, aldehydes, amines, nitriles, ethers, amides, carboxylic acids, alkynes, azoles, terpenes, pyridines, or sulfur-containing compounds. The six SPE cartridges differed in their specificity for the chemical compounds, with the XAW cartridge showing the best specificity for ketones. The greatest differences between the tested SPE cartridges appeared in the detection of specific VOCs. In total, 176 different VOCs were detected with a match factor >80%. The greatest number of specific VOCs was captured by XAW (149), followed by ENV (118), HLB (117), HRP (115), HRX (114), and XCW (114). We conclude that the tested SPE cartridges are suitable for VOC sampling from exhaled cow breath, but the SPE cartridge choice enormously affects the detected chemical groups and the number of detected VOCs. Therefore, an appropriate SPE adsorbent cartridge should be selected according to our proposed inclusion criteria. For targeted metabolomics approaches, the SPE cartridge choice depends on the VOCs or chemical compound groups of interest based on our provided VOC list. For untargeted approaches without information on the animals' metabolic condition, we suggest using multi-sorbent SPE cartridges or multiple cartridges per animal.

Sprayed Urine Emits a Pungent Odor due to its Increased Adhesion to Vertical Objects via Urinary Proteins Rather Than to Changes in its Volatile Chemical Profile in Domestic Cats

Spraying urine on vertical objects by raising the tail is a commonly observed functional behavior for chemical communication in Felidae species, including domestic cats (Felis silvestris catus). The sprayed urine is recognized as a chemical signal for territorial ownership of their habitats. Previous studies reported that sprayed urine emits a more pungent odor than urine excreted from a squatting position. However, little is known about how sprayed urine acts as a strong scent mark in the environment. Here, we showed that sprayed urine originates only from bladder urine without any secretions, such as anal sac secretions, but it can effectively emit volatile organic compounds (VOCs) when smeared on vertical objects due to its strong adhesion. Chemical profiles of VOCs and odor qualities were similar between fresh sprayed urine and bladder urine sampled immediately after spraying from the same individuals. Meanwhile, feline-specific proteinuria arising from excretion of a carboxylesterase that produces a precursor of cat-specific odorants resulted in reduced surface tension of the urine and increased adhesion to vertical surfaces, which kept sprayed urine on the surfaces and led to the emission of large amounts of VOCs. In conclusion, proteinuria contributes to the emission of a strong odor through its enhanced adhesion to vertical objects without other secretions containing malodorous substances. These findings improve our understanding of the mechanism of scent marking via the spraying of urine for chemical communication in cats.

Watching Paint Dry: Organic Vapor Emissions from Architectural Coatings and their Impact on Secondary Organic Aerosol Formation

Emissions from volatile chemical products (VCPs) are emerging as a major source of anthropogenic secondary organic aerosol (SOA) precursors. Paints and coatings are an important class of VCPs that emit both volatile and intermediate volatility organic compounds (VOCs and IVOCs). In this study, we directly measured I/VOC emissions from representative water- (latex) and oil-based paints used in the U.S. Paint I/VOC emissions vary by several orders of magnitude by both the solvent and gloss level. Oil-based paints had the highest emissions (>10⁵ μg/g-paint), whereas low-gloss interior paints (Flat, Satin, and Semigloss) all emitted ∼10² μg/g-paint. Emissions from interior paints are dominated by VOCs, whereas exterior-use paints emitted a larger fraction of IVOCs. Extended emission tests showed that most I/VOC emissions occur within 12-24 h after paint application, though some paints continue to emit IVOCs for 48 h or more. We used our data to estimate paint I/VOC emissions and the subsequent SOA production in the U.S. Total annual paint I/VOC emissions are 48-155 Gg (0.15-0.48 kg/person). These emissions contribute to the formation of 2.2-7.5 Gg of SOA annually. Oil-based paints contribute 70-98% of I/VOC emissions and 61-99% of SOA formation, even though they only account for a minority of paint usage.

Detection of the Freshness of Kiwifruit with a TD-GC-MS and a Gas-sensing Array Based on the Surface-acoustic-wave Technique

An electronic nose is an arrayed gas sensor mimicking the human olfactory system that can analyze and identify a flavour on collecting an odour from an environment. In our experiments, an electronic-nose system based on a surface acoustic wave (SAW) was used to measure the freshness of kiwifruit. 128° YX-LiNbO3 acted as a piezoelectric material; Au was deposited as an electrode and sensing area. With a polymer coating of various types on the sensing area and a connection to an oscillator circuit, a 113-114 MHz SAW was obtained. Depending on the properties of varied polymers, the frequency shift varied due to absorbed volatile organic compounds (VOC). In this way, with four surface-acoustic-wave sensors coated with varied polymers we built a kiwi-flavour database according to results from a TD-GC-MS system. When the concentration of esters increased, the kiwifruit began to ripen, accompanied by increased concentrations and types of VOC. As a result, polystyrene (PS) and fluoropolymer (CYTOP) polymers, which played the role of sensing materials, served as major materials to determine the ester aroma profile. Polyvinyl alcohol (PVA), polyvinyl butyral (PVB) and poly-N-vinylpyrrolidone (PNVP) were used to trap the alcohols and acids during a kiwifruit ripening period. This research proved that discrimination of differences is feasible from an unripe stage to a ripe stage and from a ripe stage to an over-ripe stage.

Selective formaldehyde detection at ppb in indoor air with a portable sensor

Formaldehyde is a carcinogenic indoor air pollutant emitted from wood-based furniture, building materials, paints and textiles. Yet, no low-cost sensor exists for on-site monitoring to fulfill stringent current and upcoming (e.g., 8 parts-per-billion by volume, ppb, in France by 2023) exposure guidelines. Here, we present an inexpensive and handheld formaldehyde detector with proven performance in real indoor air. Selectivity is achieved by a compact packed bed column of nanoporous polymer sorbent that separates formaldehyde from interferants present in ambient air. Downstream, a highly sensitive nanoparticle-based chemoresistive Pd-doped SnO₂ sensor detects formaldehyde in the relevant concentration range down to 5 ppb within 2 min. As a proof-of-concept, we measured formaldehyde in indoor air and from different wood product emissions, in excellent agreement (R² > 0.98) with high-resolution proton-transfer-reaction time-of-flight mass spectrometry. This detector is simple-in-use and readily applicable for on-site formaldehyde exposure monitoring at home or work. It is promising for internet-of-things (IOT) sensing networks or even wearables for personal exposure assessment.

Challenges of fast sampling of volatiles for thermal desorption gas chromatography - mass spectrometry

Fast active sampling of volatile organic compounds (VOCs) under field conditions still is a great challenge especially when the exposure time to the source of emissions is a restricting factor. Hence, to identify ideal conditions for such applications, we systematically compared fast active sampling of VOCs collected on two common adsorbents under two regimes: first, very low gas volumes (from 300 mL) sampled at nominal flow rate and, second, sampling at the maximal applicable flow rate (0.5 L/min) before loss of sorbent material was experienced. For XAD-2 and Tenax TA, efficient sorbents for on-site VOC-sampling followed by thermal desorption GC-MS, significant differences in the signal response of volatile compounds were related not only to the varied experimental factors alone, but also to their interactions and to compound volatility. In the first regime, volatiles (∼0.004-3.13 mM) from Tenax TA gave the highest signal response only above 800 mL sampled gas volume while at low concentrations (∼0.004-0.12 mM), satisfactory recovery from XAD-2 required longer analyte-sorbent interaction. For the second regime, the relative recovery was severely impaired down to 73 ± 23%, n = 56 for Tenax TA and 72 ± 17%, n = 56 for XAD-2 at intermediate concentration, and 79 ± 11%, n = 84 for Tenax TA at high concentration compared to the relative recovery at standard flow rate. Neither Tenax TA nor XAD-2 provided a 100% total recovery (calculated using breakthrough values) for any of the evaluated compounds. Finally, two-way and three-way interactions identified in a multi-variable model, explained not only the dependence of the signal response on different experimental variables, but also their complex interplay affecting the recovery of the VOCs. In conclusion, we show for the first time that XAD-2, a material only recently introduced for the adsorption of volatiles from the gas phase, competes well with the standard material Tenax TA under conditions of fast sampling. Due to the similar absolute recovery with Tenax TA even at low concentration and with regard to the better detection limits, we consider XAD-2 the better choice for fast sampling of VOCs, particularly with low sample volumes at regular flow. For fast sampling with high flow rate, however, both sorbents might be selected only if the corresponding recovery loss can be accepted for the study.

Recovery and reactivity of polycyclic aromatic hydrocarbons collected on selected sorbent tubes and analyzed by thermal desorption-gas chromatography/mass spectrometry

This article describes the optimization of methodology for extending the measurement of volatile organic compounds (VOCs) to increasingly heavier polycyclic aromatic hydrocarbons (PAHs) with a detailed focus on recent sorbent tube technology. Although PAHs have lower volatility than compounds such as benzene, toluene, ethylbenzene and xylenes, these semi-volatile compounds can be detected in air and breath samples. For this work, PAHs were captured on sorbent tubes and subsequently analyzed using automated thermal desorption gas chromatography - mass spectrometry (ATD-GC/MS). While many different sorbent tubes are commercially available, optimization for airborne PAH sampling using sorbent tubes has not been previously considered. Herein, several commercially available sorbent tubes, including Carbograph 2 TD/1TD, Tenax TA, XRO-440, and inert-coated PAH tubes are compared to determine the relative recovery for eight PAHs commonly found in the environment. Certain types of sorbent materials were found to be better suited for PAH recovery during thermal desorption, and PAH reaction products were observed on several types of sorbent tubes, including graphitized carbon black sorbents with stainless steel tube materials. As such, selection of sorbent tube media should be carefully considered prior to embarking on a PAH study.

Analytical procedure for the determination of very volatile organic compounds (C3-C6) in indoor air

The substance group of very volatile organic compounds (VVOCs) is moving into the focus of indoor air analysis, facing ongoing regulations at international and European levels targeting on indoor air quality and human health. However, there exists at present no validated analysis for the identification and quantification of VVOCs in indoor air. Therefore, the present study targeted on the development of an analytical method in order to sample the maximum possible quantity of VVOCs in indoor air on solid sorbents with subsequent analysis by thermal desorption and coupled gas chromatography/mass spectrometry (TDS-GC/MS). For this purpose, it was necessary to investigate the performance of available sorbents and to optimize the parameters of GC/MS analysis. Stainless steel tubes filled with Carbograph 5TD were applied successfully for low-volume sampling (2-4 l) with minimal breakthrough (< 1%). With the developed method, VVOCs between C₃ and C₆ of different volatility and polarity  can be detected even in trace quantities with low limits of quantitation (LOQ; 1-3 μg m^-3). Limitations occur for low molecular weight compounds ≤C₃, especially for polar substances, such as carboxylic acids and for some aldehydes and alcohols. Consequently, established methods for the quantification of these compounds in indoor air cannot be fully substituted yet. At least three different analytical techniques are needed to cover the large spectrum of relevant VVOCs in indoor air. In addition, unexpected reaction products might occur and need to be taken into account to avoid misinterpretation of chromatographic signals. Graphical abstract Solid sorbent sampling of VVOCs (C₃-C₆) in indoor air with subsequent TDS-GC/MS analysis.

Suitability of different containers for the sampling and storage of biogas and biomethane for the determination of the trace-level impurities--A review

The traceable and accurate measurement of biogas impurities is essential in order to robustly assess compliance with the specifications for biomethane being developed by CEN/TC408. An essential part of any procedure aiming to determinate the content of impurities is the sampling and the transfer of the sample to the laboratory. Key issues are the suitability of the sample container and minimising the losses of impurities during the sampling and analysis process. In this paper, we review the state-of-the-art in biogas sampling with the focus on trace impurities. Most of the vessel suitability studies reviewed focused on raw biogas. Many parameters need to be studied when assessing the suitability of vessels for sampling and storage, among them, permeation through the walls, leaks through the valves or physical leaks, sorption losses and adsorption effects to the vessel walls, chemical reactions and the expected initial concentration level. The majority of these studies looked at siloxanes, for which sampling bags, canisters, impingers and sorbents have been reported to be fit-for-purpose in most cases, albeit with some limitations. We conclude that the optimum method requires a combination of different vessels to cover the wide range of impurities commonly found in biogas, which have a wide range of boiling points, polarities, water solubilities, and reactivities. The effects from all the parts of the sampling line must be considered and precautions must be undertaken to minimize these effects. More practical suitability tests, preferably using traceable reference gas mixtures, are needed to understand the influence of the containers and the sampling line on sample properties and to reduce the uncertainty of the measurement.

Tracing hidden herbivores: time-resolved non-invasive analysis of belowground volatiles by proton-transfer-reaction mass spectrometry (PTR-MS)

Root herbivores are notoriously difficult to study, as they feed hidden in the soil. However, root herbivores may be traced by analyzing specific volatile organic compounds (VOCs) that are produced by damaged roots. These VOCs not only support parasitoids in the localization of their host, but also may help scientists study belowground plant-herbivore interactions. Herbivore-induced VOCs are usually analyzed by gas-chromatography mass spectrometry (GC-MS), but with this off-line method, the gases of interest need to be preconcentrated, and destructive sampling is required to assess the level of damage to the roots. In contrast to this, proton-transfer-reaction mass spectrometry (PTR-MS) is a very sensitive on-line, non-invasive method. PTR-MS already has been successfully applied to analyze VOCs produced by aboveground (infested) plant parts. In this review, we provide a brief overview of PTR-MS and illustrate how this technology can be applied to detect specific root-herbivore induced VOCs from Brassica plants. We also specify the advantages and disadvantages of PTR-MS analyses and new technological developments to overcome their limitations.

Proton-transfer reaction mass spectrometry (PTRMS) in combination with thermal desorption (TD) for sensitive off-line analysis of volatiles

RATIONALE

When performing trace gas analysis, it is not always possible to bring the source of volatiles and the gas analyzer together. In these cases, volatile storage containers, such as thermal desorption (TD) tubes, can be used for off-line measurement. TD is routinely combined with gas chromatography/mass spectrometry (GC/MS), but so far not with proton-transfer reaction mass spectrometry (PTRMS), which has a faster response.

METHODS

A PTR-quadrupole-MS instrument and a PTR-ion-trap-MS instrument were separately coupled to a TD unit for off-line analysis of trace volatiles in air. Carbograph 1TD/Carbopack X sorbent tubes were filled with different concentrations of a trace gas mixture containing low molecular weight volatiles (32 g/mol up to 136 g/mol) and measured with the above-mentioned combinations. The carrier gas in the TD unit was changed from helium to nitrogen to be able to combine this instrument with the mass spectrometer.

RESULTS

Good linearity and reproducibility with the amount of gas stored were obtained. The storage capacity over time (up to 14 days) showed larger variability (<11% for all compounds, except for acetone 27%). Several tubes were filled with breath of different persons, and the breath of a smoker showed increased levels of acetonitrile and benzene. The combination of the PTR ion-trap instrument with the TD unit was also investigated. Due to its higher sampling rate, the ion-trap system showed higher throughput capabilities than the quadrupole system.

CONCLUSIONS

The combination of TD with PTRMS using both a quadrupole and an ion trap for off-line volatile analysis has been validated. TD tubes can be a robust and compact volatile storage method when the mass spectrometry and the sampling cannot be performed in the same place, for example in large screening studies. In addition, a higher measurement throughput than with GC/MS could be obtained.

Evaluation of the effect of different sampling time periods and ambient air pollutant concentrations on the performance of the Radiello diffusive sampler for the analysis of VOCs by TD-GC/MS

The effect of different sampling exposure times and ambient air pollutant concentrations on the performance of Radiello® samplers for analysis of volatile organic compounds (VOCs) is evaluated. Quadruplicate samples of Radiello® passive tubes were taken for 3, 4, 7 and 14 days. Samples were taken indoors during February and March 2010 and outdoors during July 2010 in La Canonja (Tarragona, Spain). The analysis was performed by automatic thermal desorption (ATD) coupled with capillary gas chromatography (GC)/mass spectrometry detection (MS). The results show significant differences (t-test, p < 0.05) between the amounts of VOCs obtained from the sum of two short sampling periods and a single equivalent longer sampling period for 65% of all the data. 17% of the results show significantly larger amounts of pollutant in the sum of two short sampling periods. Back diffusion due to changes in concentrations together with saturation and competitive effects between the compounds during longer sampling periods could be responsible for these differences. The other 48% of the results that are different show significantly larger amounts in the single equivalent longer sampling period. The remaining 35% of the results do not show significant differences. Although significant differences are observed in the amount of several VOCs collected over two shorter sampling intervals compared to the amount collected during a single equivalent longer sampling period, the ratios obtained are very close to unity (between 0.7 and 1.2 in 75% of cases). We conclude that Radiello® passive samplers are useful tools if their limitations are taken into account and the manufacturer's recommendations are followed.

Comparison of two methods of measuring wood pyrolysis tar

Two methods for the sampling and analysis of tar produced from wood pyrolysis were compared. The first method used a conventional cold-trapping technique in solvent-filled impingers followed by liquid injection. The second one is a new application of multibed solid-phase adsorbent (SPA) tubes followed by thermal desorption (TD). Both methods are based on gas chromatography (GC) coupled with mass spectrometry (MS). Quantification was performed with a well reproducible GC-MS method with three internal deuterated standards. The SPA/TD method offers several advantages. No solvent is required, the detection levels are improved, and gas chromatography separation is easier. Moreover, sampling time is reduced from about 1h (for the conventional cold-trapping technique in impingers) to a few seconds. No discrimination was observed between the two sampling methods for the 10 quantified compounds (aromatic compounds from benzene to phenanthrene and phenols) except for benzene.

Differences between Alveolar Air and Mouth Air

Our breath contains an intraoral and an alveolar part, the latter being the last to be exhaled. As such, major differences in composition can be expected, with for alveolar air the inclusion of more metabolic compounds released during the blood-air exchange. This study explored the differences between breath air from the oropharynx and from the lungs in healthy volunteers. Mouth and alveolar air of 40 volunteers was analyzed using gas chromatography-mass spectrometry, together with a sample of room air. A chromatogram of a single person contains on average 145 different compounds. Altogether, 618 compounds were detected. A total of 35 compounds were common to all volunteers. The number of compounds was significantly higher in mouth air than in alveolar air. For 47 compounds, very significant differences in detection/concentration were recorded. Gas chromatography-mass spectrometry offers a detailed overview of the compounds in a person's breath. One should be aware of the distinction between alveolar air and oropharyngeal air.

Analysis of amides in the air by sampling with SPME and detection by GC-FID

This paper proposes a solid-phase microextraction (SPME) method for the passive sampling and determination of N,N-dimethylacetamide (DMA) and N,N-dimethylformamide (DMF) in air by capillary GC with flame ionization detection. The optimized conditions for SPME method were grab sampling, polydimethylsiloxane/divinylbenzene fiber, extraction for 90 min at 25 +/- 2 degrees C, desorption for 3 min at 220 degrees C, and relative humidity 45 +/- 2%. Under these conditions, the method presented good linearity (R = 0.996), repeatability (%RSD 2.79 and 9.85 for DMF and DMA, respectively), and detection limit (0.021 and 0.024 mg/m3 for DMF and DMA, respectively).

Advances and challenges in the identification of volatiles that mediate interactions among plants and arthropods

The relatively new research field of Chemical Ecology has, over the last two decades, revealed an important role of plant-produced volatile organic compounds (VOCs) in mediating interactions between plants and other organisms. Of particular interest are the volatile blends that plants actively emit in response to herbivore damage. Various efforts are underway to pinpoint the bioactive compounds in these complex blends, but this has proven to be exceedingly difficult. Here we give a short overview on the role of herbivore-induced plant volatiles in interactions between plants and other organisms and we review methods that are currently employed to collect and identify key volatile compounds mediating these interactions. Our perspective on future directions of this fascinating research field places special emphasis on the need for an interdisciplinary approach. Joint efforts by chemists and biologists should not only facilitate the elucidation of crucial compounds, but can also be expected to lead to an exploitation of this knowledge, whereby ecological interactions may be chemically manipulated in order to protect crops and the environment.

In situ modification of herbivore-induced plant odors: a novel approach to study the attractiveness of volatile organic compounds to parasitic wasps

Many parasitic wasps (parasitoids) exploit volatile organic compounds (VOCs) emitted by herbivore-infested plants in order to locate their hosts, but it remains largely unknown which specific compounds within the volatile blends elicit the attractiveness to parasitoids. One way of studying the importance of specific VOCs is to test the attractiveness of odor blends from which certain compounds have been emitted. We used this approach by testing the attraction of naive and experienced females of the two parasitoids Cotesia marginiventris and Microplitis rufiventris to partially altered volatile blends of maize seedlings (Zea mays var. Delprim) infested with Spodoptera littoralis larvae. Adsorbing filter tubes containing carbotrap-C or silica were installed in a four-arm olfactometer between the odor source vessels and the arms of the olfactometer. The blends breaking through were tested for chemical composition and attractiveness to the wasps. Carbotrap-C adsorbed most of the sesquiterpenes, but the breakthrough blend remained attractive to naive C. marginiventris females. Silica adsorbed only some of the more polar VOCs, but this essentially eliminated all attractiveness to naive C. marginiventris, implying that among the adsorbed compounds there are some that play key roles in the attraction. Unlike C. marginiventris, M. rufiventris was still attracted to the latter blend, showing that parasitoids with a comparable biology may employ different strategies in their use of plant-provided cues to locate hosts. Results from similar experiments with modified odor blends of caterpillar-infested cowpea (Vigna unguiculata) indicate that key VOCs in different plant species vary greatly in quality and/or quantity. Finally, experienced wasps were more strongly attracted to a specific blend after they perceived the blend while ovipositing in a host. Considering the high number of distinct adsorbing materials available today, this in situ modification of complex volatile blends provides a new and promising approach pinpointing on key attractants within these blends. Advantages and disadvantages compared to other approaches are discussed.

Thermogravimetric calibration of permeation tubes used for the preparation of gas standards for air pollution analysis

Sources of VOC (Volatile Organic Compounds) reference-materials at ppm and ppb levels are needed for calibration of air monitoring instruments. The permeation-tube technique is considered effective for the preparation of low concentration standards of high accuracy and stability. In this work, purpose-built PTFE permeation tubes, containing benzene, toluene, ethylbenzene, o-xylene or m-xylene (BTEX) were accurately and rapidly calibrated. Using the sensitive thermo-balance of a thermogravimetric apparatus, very low permeation rates were determined by the continuous monitoring of the tube weight loss as a function of time. Permeation rates in the range from 25 to 350 ng min(-1) were determined with precision. Thermogravimetry appears to be a rapid method for the measurement of weight loss at constant temperature, allowing rapid characterization and recalibration of permeation tubes. A detailed study on toluene, chosen as a typical case, showed that there are variations of the permeation rate in the long term. The temperature dependence of the permeation coefficient was also explored and permeation rates were shown to display an Arrhenius behavior in the temperature range 304-324 K. Thermodynamic parameters influencing the permeation were discussed.

Semicontinuous GC analysis and receptor modelling for source apportionment of ozone precursor hydrocarbons in Bresso, Milan, 2003

The European Ozone Directive 2002/3/EC specifies the analysis of 30 individual C2-C9 hydrocarbons in urban air with the attribution of emission sources to pollution concentrations as a major objective. In the present study, we investigate an approach for source apportionment of these ozone precursor hydrocarbons in urban air based on reliable semi continuous volatile organic compound (VOC) analysis in the field and in vehicle emission laboratory combined with multivariate receptor modeling. The GC system relies on an hourly analytical cycle based on a trap sample enrichment phase followed by a dual column gas chromatographic flame ionisation detector (FID) analysis and has successfully been tested during an air monitoring campaign at an urban site (Milan, Italy, September 2003) and in the vehicle laboratory performing exhaust emission measurements while running driving cycles on a chassis dynamometer (mopeds, gasoline and diesel cars). The receptor modeling relies on two complementary principles. The chemical mass balance (CMB) modeling apportions well characterized source profiles for the 30 individual C2-C9 hydrocarbons in the Ozone Directive to the concentrations in ambient air and produces source contribution estimates (SCE) as output. The positive matrix factorization (PMF) analyses variability in the ambient air concentration data and searches for latent variables consisting of co-varying hydrocarbons and produces profiles as output, which in this study could be attributed to known emission sources. Both CMB and PMF rely on an estimated uncertainty for each input data. A new approach is presented, by which the uncertainty is allowed to float as function of the photochemical reactivity of the atmosphere and the stability of each individual compound.

On-line multi-bed sorption trap for VOC analysis of large-volume vapor samples: injection plug width, effects of water vapor and sample decomposition

A multibed on-line sorption trap is used to preconcentrate organic vapors from air samples and inject the analytes into a GC separation column. Injection plug widths depend on the boiling point for the lipophilic compounds and on the polarity and boiling point for the polar compounds. Injection plug widths are sufficiently small (0.7-0.8 s) as to allow the direct injection of the most volatile compounds into the GC column without the need for a second focusing device. The presence of water in the samples has an effect on the retention of polar compounds by the trap. However, this effect is reproducible for a fixed water content and so can be overcome by using calibration standards under the same conditions of humidity as the samples. The thermal decomposition of many volatile organic compounds in an on-line sorption trap during the GC analysis of air samples is examined. The results show that degradation of unstable compounds is governed by the amount of heat transferred to the compounds during desorption (i.e., applied temperature and pulse duration). The use of an on-line trap results in the immediate transfer of desorbed compounds to the analytical column, which can reduce the formation of artifacts.

Wet effluent diffusion denuder technique and the determination of volatile organic compounds in air. II. Monoterpenes

The wet effluent diffusion denuder technique (WEDD), for the determination of alpha- and beta-pinenes, S-limonene, alpha-phellandrene, camphene and delta3-carene in air has been tested. These monoterpenes were continuously preconcentrated into a thin film of methanol (ethanol, 1-propanol and heptane) flowing down the inner wall of the cylindrical wet effluent diffusion denuder. The concentrates were analyzed by GC-FID and GC-MS, respectively.

Sorbent trapping of volatile organic compounds from air

The use of sorbents in trapping volatile organic compounds in air for subsequent analysis is reviewed. Sorbents are classified in accordance with the mechanism used to recover the trapped compounds, either solvent or thermal desorption. The use of sorbents is contrasted with other sampling procedures, such as collecting whole air samples using canisters. New developments such as solid-phase microextraction are described. In particular, emphasis is placed on a holistic approach to sampling and analysis, and communication is encouraged between those who take samples in the field, and those who perform the analysis.

Characterization of a commercial gas chromatography-flame ionization detection system for the in situ determination of C5-C10 hydrocarbons in ambient air

A commercial automated gas chromatograph with preconcentration on solid adsorbents (AirmoVoc HC1010) was coupled with a mass spectrometer in parallel with the flame ionization detection (FID) system and characterized for its suitability for quasi continuous measurements of atmospheric hydrocarbons (HCs) with a time resolution of 20 min. Of the 50 identified HCs in the range C5-C10, 15 elute in isolated peaks and 20 in groups of two or more HCs. The remaining 15 HCs suffer from coelution by oxygenated and halogenated compounds. Procedures to minimize and quantify the blanks and the memory from the adsorbents are described. Calibration was based on a custom-made diffusion source. The accuracy of this calibration (+/-10%, 2sigma) was verified by analysis of a certified 70-component standard (average deviation: -4.3+/-2%). During a field experiment in Summer 1998, the HC1010 system was compared with a custom-made GC system with cryogenic preconcentration and much better separation properties but lower time resolution. In ambient air, good agreement (2sigma deviation <14% or 10 ppt) was found for HCs and groups of HCs that are free from coelution with oxygenated compounds, whereas large discrepancies (in some cases more than a factor of three) were found for those HCs that coelute with oxygenated compounds, as identified by MS. Analysis of the mass spectra from those peaks via specific target ions showed much better agreement with the FID system of the reference GC within 25%.

Air analysis using tenax collection with jet-separator enrichment and ion trap mass spectrometric analysis

A dual adsorbent trap inlet system has been developed for an ion trap mass spectrometer (ITMS) to provide a rapid and sensitive system for screening of volatile organic compounds in air. The system employs three stages of concentration: preconcentration on an adsorbent Tenax trap, focusing in a cryogenic collection trap, and jet separator enrichment immediately prior to analysis by ITMS. Ten minute integrated samples are collected and analyzed immediately. The detection limit is 0. 9 parts-per-trillion by volume (pptrv) based on toluene as the analyte, and the reproducibility is 2% or better. Ambient air was analyzed for toluene on April 4, 1996 in Los Alamos, New Mexico, and concentrations ranged from 11-158 pptrv.