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PubMed2006

Colorimetric sensor arrays for volatile organic compounds.

The development of a low-cost, sensitive colorimetric sensor array for the detection and identification of volatile organic compounds (VOCs) is reported. Using an array composed of chemoresponsive dyes, enormous discriminatory power is possible in a simple device that can be imaged easily with an ordinary flatbed scanner. Excellent differentiation of closely related organic compounds can be achieved, and a library of 100 VOCs is presented. The array discriminates among VOCs by probing a wide range of intermolecular interactions, including Lewis acid/base, Brønsted acid/base, metal ion coordination, hydrogen bonding, and dipolar interactions. Importantly, by proper choice of dyes and substrate, the array is essentially nonresponsive to changes in humidity.

Biosensing Techniques↗

PubMed2002

Dynamic air sampling of volatile organic compounds using solid phase microextraction.

A new dynamic air sampling system was devised and evaluated in conjunction with solid phase microextraction (SPME) fiber materials for extracting odor-causing volatile organic compounds (VOCs) present in swine building environments. Utilizing a standard solution consisting of 11 compounds (i.e., volatile fatty acids, indoles, and phenol), sampling times, volumes, and flow rates were adjusted to establish optimal extraction conditions. Results indicated that the sampling system was effective with the Carboxen/Polydimethylsiloxane (CAR/PDMS) fiber in extracting all 11 standard compounds. The best sampling conditions for the extraction were a 100-mL sampling vial subjected to a continuous flow of 100 mL/min for 60 min. The gas chromatographic analysis showed that the reproducibility was within acceptable ranges for all compounds (RSD=4.24-17.26% by peak areas). In addition, field tests revealed that the sampling system was capable of detecting over 60 VOCs in a swine house whose major components were identified by gas chromatography-mass spectrometry (GC-MS) and by their retention times as volatile fatty acids, phenols, indole, and skatole. The field tests also showed that considerably different levels of VOCs were present in various parts of the swine building.

Air Pollutants↗

PubMed2004

A novel personal air sampling device for collecting volatile organic compounds: a comparison to charcoal tubes and diffusive badges.

Evacuated canisters have been used for many years to collect ambient air samples for gases and vapors. Recently, significant interest has arisen in using evacuated canisters for personal breathing zone sampling as an alternative to sorbent sampling. A novel flow control device was designed and built at McGill University. The flow control device was designed to provide a very low flow rate, <0.5 mL/min, to allow a sample to be collected over an extended period of time. Previous experiments run at McGill have shown agreement between the mathematical and empirical models to predict flow rate. The flow control device combined with an evacuated canister (capillary flow control-canister) was used in a series of experiments to evaluate its performance against charcoal tubes and diffusive badges. Air samples of six volatile organic compounds were simultaneously collected in a chamber using the capillary flow control-canister, charcoal tubes, and diffusive badges. Five different concentrations of the six volatile organic compounds were evaluated. The results from the three sampling devices were compared to each other and to concentration values obtained using an online gas chromatograph (GC). Eighty-four samples of each method were collected for each of the six chemicals. Results indicate that the capillary flow control-canister device compares quite favorably to the online GC and to the charcoal tubes, p > 0.05 for most of the tests. The capillary flow control-canister was found to be more accurate for the compounds evaluated, easier to use, and easier to analyze than charcoal tubes and passive dosimeter badges.

Air Movements↗

PubMed2002

Photocatalytic degradation of volatile organic compounds at the gas-solid interface of a TiO2 photocatalyst.

In the present work, photocatalytic degradation of volatile organic compounds including gas-phase trichloroethylene (TCE), acetone, methanol and toluene over illuminated TiO2 was closely examined in a batch photoreactor as a function of water vapor, molecular oxygen and reaction temperature. Water vapor enhanced the photocatalytic degradation rate of toluene, but was inhibitive for acetone, and, there was an optimum water vapor concentration in the TCE and methanol removal. In a nitrogen atmosphere, it showed lower photocatalytic degradation rate than in air and pure oxygen. Thus, it could be concluded that oxygen is an essential component in photocatalytic reactions by trapping photogenerated electrons on the semiconductor surface and by decreasing the recombination of electrons and holes. As for the influence of reaction temperature, it was found that photocatalytic degradation was more effective at a moderate temperature than at an elevated temperature for each compound.

Acetone↗

PubMed2006

Study of preservation of polydimethylsiloxane/Carboxen solid-phase microextraction fibres before and after sampling of volatile organic compounds in indoor air.

Solid-phase microextraction (SPME) was applied to the on-site analysis of volatile organic compounds (VOCs) in indoor air. The compounds were at trace levels, which complicates analysis and also sample storage. Fibre storage before and after sampling was studied. Several tests were performed, and the best results were obtained for a home-made storage assembly. To avoid contamination by acetone and acetaldehyde, activated carbon was added in the storage housing. Under these conditions, fibres can be stored up to 2 days before use. After sampling, storage of 10 VOCs was evaluated by varying air relative humidity of the air. This parameter was shown to be insignificant for 3 storage days: recoveries for acetaldehyde and acetone were 149 and 176%, respectively, and ranged from 95 to 107% for the other VOCs investigated.

Air Pollutants↗

PubMed2003

Compound-specific carbon isotope analysis of volatile organic compounds in the low-microgram per liter range.

Compound-specific carbon isotope analysis (CSIA) has become an important tool in biological, archeological, and geological studies as well as in forensics, food sciences, and organic chemistry. If sensitivity could be enhanced, CSIA would further have an improved potential for environmental applications such as, for example, in situ remediation studies to assess contaminated environments, identification of pollutant degradation pathways and kinetics, distinction between degradation/formation mechanisms, or, verification of contaminant sources. With this goal in mind, we have developed methods to determine delta13C values of commonly reported groundwater contaminants in low-microgram per liter concentrations. Several injection and preconcentration techniques were evaluated for this purpose, i.e., on-column injection, split/ splitless injection, solid-phase microextraction (SPME), and purge and trap (P&T) in combination with gas chromatography-isotope ratio mass spectrometry. The delta13C values of the target compounds were determined by liquid injections of the analytes dissolved in diethyl ether or, in the case of P&T and SPME, by extraction from water spiked with the analytes. P&T extraction was the most efficient preconcentration technique reaching method detection limits (MDLs) from 0.25 to 5.0 microg/L. These are the lowest MDLs reported so far for continuous-flow isotope ratio determinations, using a commercially available and fully automated system. Isotopic fractionation resulting from preconcentration and injection was investigated and quantified for the priority groundwater pollutants methyl tert-butyl ether (MTBE), chloroform, tetrachloromethane, chlorinated ethylenes, benzene, and toluene. The isotopic fractionations caused by the extraction techniques were small but highly reproducible and could therefore be corrected for. P&T was characterized by a higher reproducibility and smaller isotopic fractionations than SPME. Among the liquid injection techniques, cold on-column injection resulted in slightly better precision compared to split/splitless injection. However, the MDLs determined for liquid injections were 4-6 orders of magnitude higher (i.e., 9.5-2800 mg/L) than for P&T and SPME. Since both of the latter methods are solventless, a better chromatographic resolution was obtained than for the liquid injection techniques. The P&T and SPME methods described here are also applicable for CSIA of D/H ratios, which require 10-20 times higher analyte concentrations than 13C/12C analysis. Finally, the applicability of the described methods is demonstrated for pollutant concentrations of only 5-60 microg/L in environmental samples.

Journal Article↗

PubMed2005

Unambiguous identification of volatile organic compounds by proton-transfer reaction mass spectrometry coupled with GC/MS.

Interest in on-line measurements of volatile organic compounds (VOCs) is increasing, as sensitive, compact, and affordable direct inlet mass spectrometers are becoming available. Proton-transfer reaction mass spectrometry (PTR-MS) distinguishes itself by its high sensitivity (low ppt range), high time resolution (200 ms), little ionization-induced fragmentation, and ionization efficiency independent of the compound to be analyzed. Yet, PTR-MS has a shortcoming. It is a one-dimensional technique that characterizes compounds only via their mass, which is not sufficient for positive identification. Here, we introduce a technical and analytical extension of PTR-MS, which removes this shortcoming, while preserving its salient and unique features. Combining separation of VOCs by gas chromatography (GC) with simultaneous and parallel detection of the GC effluent by PTR-MS and electron impact MS, an unambiguous interpretation of complex PTR-MS spectra becomes feasible. This novel development is discussed on the basis of characteristic performance parameters, such as resolution, linear range, and detection limit. The recently developed drift tube with a reduced reaction volume is crucial to exploit the full potential of the setup. We illustrate the performance of the novel setup by analyzing a complex food system.

Coffee↗

PubMed2004

An improved model for analyzing the performance of photocatalytic oxidation reactors in removing volatile organic compounds and its application.

An improved photocatalytic oxidation (PCO) reactor model was developed to analyze the removal of volatile organic compounds (VOCs) in indoor air. One new parameter, the average total removing factor Kt, together with the other two parameters, the number of mass transfer units NTUm and the fractional conversion epsilon, are found to be the main parameters influencing the photooxidation performance of PCO reactors. Three new parameters, the ideal reaction number of mass transfer units, NTUm,ir; the ideal reaction fractional conversion, epsilonir; and the reaction effectiveness, eta, also are defined. These concepts are helpful to the structural design and optimization for PCO reactors. The application of the model in designing a plate-type PCO reactor is demonstrated. This study shows that the present model is an effective tool for designing PCO reactors and for evaluating VOC removal performance of available PCO reactors.

Air Pollution, Indoor↗

PubMedDate not supplied

Volatile organic compound fate in phytoremediation applications: natural and engineered systems.

Unique sampling techniques have generated a new understanding regarding the fate of volatile organic compounds (VOCs) in phytoremediation systems. Tissue sampling and diffusion traps were used to determine how VOCs are transported in and diffuse from vegetation, particularly woody species. These techniques were then utilized to observe how plants interact with different contaminated media, showing transport of contaminants occurs from the vadose zone (vapor phase) as well as the saturated zone (aqueous phase). Data was gathered in laboratory studies, in native vegetation, and in engineered phytoremediation systems. The findings reveal that diffusion from the xylem tissues to the atmosphere is a major fate for VOCs in phytoremediation applications. Linking VOCs' fate with groundwater hydraulics, mass removal rates from contaminant plumes can be estimated. These techniques were also utilized to observe the impact of engineered plant/microbe systems, which utilize recombinant, root-colonizing organisms to selectively degrade compounds and subsequently alter the fate of VOCs and other organic compounds. The genetically enhanced rhizoremediation methods pose a novel approach that may allow for biodegradation of compounds that formerly were considered recalcitrant.

Biodegradation, Environmental↗

PubMed2001

[Reduction of the volatility of volatile organic compounds with cyclodextrins: application to their capture].

The interactions existing between beta-cyclodextrin, hydroxypropyl-beta-cyclodextrin and six volatile organic compounds (VOC) were studied and used for capture of such pollutants. The reduction of volatility for these VOC appeared to be equivalent for the two kinds of cyclodextrins at equal concentrations, while a higher solubility conferred higher efficiency to hydroxypropyl-beta-cyclodextrin. The use of such cyclodextrins in traps allowed a two-fold increase in VOC capture compared with genuine water. Application of this process to an industrial site showed its efficacity qualitatively while several optimization procedure are needed to achieve quantitative efficacy.

Cyclodextrins↗

PubMed2000

Introduction of a sink-diffusion model to describe the interaction between volatile organic compounds (VOCs) and material surfaces.

A sink-diffusion model to describe the interaction between material surfaces and volatile organic compounds (VOCs) in indoor air has been introduced. The model is based on adsorption/desorption on the material surfaces and diffusion into the materials. Test chamber experiments with exposure of nylon carpet and polyvinyl chloride (PVC) covering against alpha-pinene and toluene were used to validate the model and to make comparisons with a sink model based on the Langmuir adsorption isotherm. The results showed that the sink-diffusion model gave a better description of the desorption curve than the Langmuir model. The model predictions improved with increasing sorption effect. The Langmuir model gave good predictions of relative weak sorption effects, whereas the sink-diffusion model improved the predictions for stronger sorption effects. In this case, nylon carpet showed substantial stronger sorption than PVC covering and alpha-pinene showed stronger sorption than toluene. Controlled field experiments with combinations of building materials and a mixture of VOCs, encountered in real indoor environments, are needed to further validate the sink-diffusion model.

Adsorption↗

PubMed2003

Direct quantitation of volatile organic compounds in packaging materials by headspace solid-phase microextraction-gas chromatography-mass spectrometry.

The quantification of volatile organic compounds (VOCs) in flexible multilayer packaging materials using headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) was studied. The analytes imclude 22 compounds such as aldehydes. ketones, carboxylic acids and hydrocarbons formed by thermooxidative degradation of polyethylene during the extrusion coating process in the manufacture of the packaging, and many of them are involved in the unpleasant and undesirable odour of these materials. External standard calibration using a solution of the analytes in an appropriate solvent was the first approach studied. Aqueous solutions of the analytes provided low reproducibility and the reduction of aldehydes to alcohols under the HS-SPME conditions. Hexadecane was chosen as the solvent since its polarity is similar to that of polyethylene and its volatility is lower than that of the analytes. However, hexadecane should be added to the sample before the analysis as it modifies the absorption capacity of the fibre. A 75-microm Carboxen-poly(dimethylsiloxane) fibre was used to extract the VOCs from the headspace above the packaging in a 15-ml sealed vial at 100 degrees C after 5 min of preincubation. The influence of the extraction time on the amount extracted was studied for a standard solution of the analytes in hexadecane, together with the influence of the volume of the standard solution and the amount of the sample placed in the vial. Standard addition and multiple HS-SPME were also studied as calibration methods and the results obtained in the quantitative analysis of a packaging material were compared.

Calibration↗

PubMed1995

Estimation of volatile organic compounds in Kuwaiti houses after the Gulf war.

Interest in indoor air quality is steadily increasing. Exposure to volatile organic compounds (VOCs) is associated with health effects as diverse as childhood respiratory disease, lung cancer and cardiovascular disease. In an effort to assess the environmental impact indoors from possible sources of VOCs, such as (i) open oil lakes, (ii) chemical and petrochemical industries and (iii) indoor pollution from household items, concentrations of aliphatic and aromatic VOCs, comprising n-hexane to n-hexadecane, benzene, toluene, xylene, ethyl benzene, methanol and o-dichlorobenzene, were measured in indoor air samples from seven different cities in Kuwait using a gas chromatograph. The data for the period March to May 1993 are presented. The VOCs, as measured, were surprisingly low and they are below the concentrations set by the American Hygienists Association. However, although the concentration of the estimated VOCs being low, were cumulative effects of them entering the human body and water sources cannot be ruled out.

Journal Article↗

PubMed2004

C1 to C9 volatile organic compound measurements in urban air.

Urban atmospheric samples were collected in A Coruna (NW Spain) and analysed for volatile organic compounds. One hundred and twenty one hour samples were collected in winter 2000. The ambient air was rich in benzene, toluene, ethyl-benzene and xylenes (BTEX) and especially toluene (mean: 23.6 microg m(-3), median: 14.66 microg m(-3)), but the presence of chlorinated compounds was also notable. High concentrations of 1,4-dichlorobenzene (mean: 11.4 microg m(-3), max: 90.4 microg m(-3)) were recorded. Multivariate analysis of VOC, trace gases (NO(x), NO(2), NO, SO(2) and O(3)) and meteorological variables (temperature, wind direction and speed, precipitation and radiation) was applied and correlations between VOC were also studied. Principal component analysis and correlation analysis confirm traffic as the main source of VOC in the area, although the importance of evaporative sources is also reflected. Three groups of samples were obtained by cluster analysis; these groups are formed depending on the content of aromatics and ozone and, in many cases, on the sampling hour.

Journal Article↗

PubMed1994

Production of blank water for the analysis of volatile organic compounds in human blood at the low parts-per-trillion level.

Blank water with low levels of volatile organic compounds (VOCs) is of critical importance in many analytical procedures. Because of the increased use of more sophisticated instrumentation, the detection limits for these compounds have dropped dramatically. Consequently, techniques in use in the analytical laboratory to generate blank water may now prove inadequate. The need for blank water with low levels of VOCs was recently underscored by the development of an analytical procedure to analyze 32 VOCs in whole blood; this procedure has detection limits in the tens of parts-per-trillion level for most VOCs. Common sources of blank water in the laboratory such as deionized, cartridge-filtered, and HPLC-grade bottled water are analyzed. These sources contained high concentrations of some VOCs that would interfere with low parts-per-trillion analyses. Well water and bottled water used for human consumption are analyzed, but both prove inadequate for the analysis of VOCs at parts-per-trillion levels. A combination of distillation and purging with helium produced blank water with VOC levels of less than 10 parts-per-trillion for most of the 16 VOCs studied.

Blood Chemical Analysis↗

PubMed1997

[Effects of mixture of 22 kinds of volatile organic compounds on human body at different temperature].

Ten healthy volunteers were exposed to mixture of 22 kinds of volatile organic compounds with concentrations of zero to 10 mg/m3 at the temperature of 18, 22 and 26 C, respectively in an artificial climate room for 60 minutes a day and six days week for two consecutive weeks to study their effects on human bodies. Results showed that quality of indoor air decreased significantly, odor intensity increased, number of the subjects who need more ventilation increased, and irritation to eyes, nose and skin intensified under the mixture concentration of 10 mg/m3 and at temperature of 26 degrees C. No significant changes in psychological tests, tear film stability and cytological studies were found. Room temperature at 26 degrees C has a significant synergetic effects on human health. Therefore, quality of indoor air can not be evaluated only by organic compounds polluted in air, but by meteorological conditions.

Adolescent↗

PubMed2006

Characterization of ceria-zirconia mixed oxides as catalysts for the combustion of volatile organic compounds using inverse gas chromatography.

Inverse gas chromatography (IGC) has been used in this work for characterizing the adsorption of different volatile organic compounds (VOCs) (1,2-dichloroethane (DCE), trichloroethylene (TCE), and n-hexane) over ceria-zirconia mixed oxides (Ce(x)Zr(1-x)O2, with x = 0, 0.15, 0.5, 0.68, 0.8 and 1). These materials have shown to be very active catalysts for the deep oxidation of the studied VOCs in previous papers. The enthalpies of adsorption (-deltaH(ads)), adsorption isotherms (corresponding to the Henry region), and dispersive (gamma(s)(D)) and specific (I(sp)) components of the surface energy for the adsorption of the investigated compounds are determined using IGC at infinite dilution. These chromatographic data and other surface parameters (surface area, oxygen storage capacity, surface acidity, and reducibility) are correlated with the activity and selectivity of these catalysts. As a result, for n-hexane, the catalytic activity is mainly correlated with the adsorption capacity of the solids, whereas the activity for chlorinated compounds oxidation (as well as the selectivity to oxidation products) depends on both oxygen storage capacity and specific interaction of the chlorinated compound with the surface.

Adsorption↗

PubMed2003

Microwave plasma conversion of volatile organic compounds.

A microwave-induced, steam/Ar/O2, plasma "torch" was operated at atmospheric pressure to determine the feasibility of destroying volatile organic compounds (VOCs) of concern. The plasma process can be coupled with adsorbent technology by providing steam as the fluid carrier for desorbing the VOCs from an adsorbent. Hence, N2 can be excluded by using a relatively inexpensive carrier gas, and thermal formation of oxides of nitrogen (NOx) is avoided in the plasma. The objectives of the study were to evaluate the technical feasibility of destroying VOCs from gas streams by using a commercially available microwave plasma torch and to examine whether significant byproducts were produced. Trichloroethene (TCE) and toluene (TOL) were added as representative VOCs of interest to a flow that contained Ar as a carrier gas in addition to O2 and steam. The O2 was necessary to ensure that undesirable byproducts were not formed in the process. Microwave power applied at 500-600 W was found to be sufficient to achieve the destruction of the test compounds, down to the detection limits of the gas chromatograph that was used in the analysis. Samples of the postmicrowave gases were collected on sorbent tubes for the analysis of dioxins and other byproducts. No hazardous byproducts were detected when sufficient O2 was added to the flow. The destruction efficiency at a fixed microwave power improved with the addition of steam to the flow that passed through the torch.

Adsorption↗