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At least 613 records · Page 34Linked to original sources

PubMed2005

[Measurement method research on trace volatile organic compounds in atmosphere].

An automated accumulation sampling system and a method of two-step Cryo-Concentrated System combined with Gas Chromatography/Mass Spectrometry (CCS-GC/MS) are introduced. The method is evaluated by a set of special experiments and the results are demonstrated. The lowest limit volume concentrations of the measurement is expanded from 10 (-6) to 10(-12) using CCS-GC/ MS instead of the normal method of GC/MS and the average response factor of 39 object compounds is 2.9 x 10(-12) x A(-1). When injection volume of air sample reaches 1000 cm3, the lowest limit is 7 x 10(-12) - 40 x 10(-12); CCS-GC/MS may identify all the objective chemical species in the atmosphere samples, with average 2.5s bias of retention time for 39 GC peaks. Within 0 - 400 x 10(-9), the concentration of all the objective compounds can be calculated by standard curve individually (average r2 above 0.99) and accurately. The recollect rate is 88% - 111%, at average of 100.8% +/- 5.6%; and the bias of precision is 2% - 14%, at average of 6.6%.

Air Pollutants↗

PubMed2000

The volatile organic compounds from the mycelium of Tuber borchii Vitt.

The mycelium of T. borchii (characterized by DNA analysis) grown in sterile liquid medium produced some VOCs. The VOCs were retained on carbographs by passing a flow of helium, isolated and characterized in a GC-MS equipment after a thermal desorption. The compounds present in the VOCs from the mycelium cultures, but not in the VOCs from the control cultures, contained 29 compounds. The main compounds were 1,3-ditertbutylbenzene (16.1 ng/l), 3-methylheptane (9.2 ng/l), butan-2-one (8.8 ng/l), ethynylbenzene (5.6 ng/l), and octan-3-one (4.9 ng/l).

Ascomycota↗

PubMed2001

Wet effluent diffusion denuder technique and determination of volatile organic compounds in air. I. Oxo compounds (alcohols and ketones).

The wet effluent diffusion denuder (WEDD) preconcentration technique for the determination of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 1-pentanol, acetone, methyl ethyl ketone, diethyl ketone and methyl n-propyl ketone in air is discussed. The compounds are continuously collected into a thin film of deionized water flowing down the inner wall of the cylindrical wet effluent diffusion denuder. The concentrate is analysed by gas chromatography. Detection limits of alcohols and ketones are as low as 1 microg/l (GC-flame ionization detection) and/or 1 ng/l (GC-MS). This technique could be applicable for the continuous monitoring of ppb (v/v) levels of both alcohols and ketones in the air.

Air↗

PubMed2000

Comparison of nutshell granular activated carbons to commercial adsorbents for the purge-and-trap gas chromatographic analysis of volatile organic compounds.

Granular activated carbons (GACs) made from agricultural by-products were investigated as adsorbents for short path thermal desorption gas chromatographic analysis of selected polar and nonpolar organic compounds. GACs made from macadamia nut, black walnut and hazelnut shells were compared to four commercially available adsorbents, namely, Tenax TA, Carboxen 569, Carbosieve SIII and coconut charcoal for their properties in purge-and-trap analysis. Adsorption values and breakthrough volumes were calculated for compounds from C3 and C6-C10. GACs derived from macadamia nut shells were found to adsorb and desorb between 80% (benzene) and 277% (ethylbenzene) more acetone (C3), benzene (C6), toluene (C7), ethyl- (C8), n-propyl- (C9), or sec.-butylbenzenes (C10) purged from water at the 100 ppb level than the commercial adsorbents tested.

Adsorption↗

PubMed2001

Evaluating competitive sorption mechanisms of volatile organic compounds in soils and sediments using polymers and zeolites.

The competitive sorption of trichloroethene (TCE) and tetrachloroethene (PCE) was investigated in three natural solids, two polymers, and four zeolites. Competition was observed in natural solids with high contents of recalcitrant organic carbon, in the glassy polymer, and in zeolites with strongly and moderately hydrophobic micropores of large (7.5 x 10 A) and small pore widths (approximately 5.4 A), respectively. Isotherm results and recalcitrant OC% values for natural solids indicate that the extent of competition between TCE and PCE is related to the amount of hard organic carbon. Gas adsorption results and the variability in C/H values suggest that natural organic matter contains micropores with varying width and polarity. Isotherm results for zeolites indicate that competition between TCE and PCE increases with increasing hydrophobicity and decreasing micropore width. We suggest that competition between volatile organic contaminants in the subsurface is controlled by competition for hydrophobic micropores in hard organic matter and that smaller more hydrophobic micropores result in stronger competition.

Adsorption↗

PubMed2002

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.

Chromatography, Gas↗

PubMedDate not supplied

Natural attenuation of volatile organic compounds (VOCs) in the leachate plume of a municipal landfill: using alkylbenzenes as process probes.

More than 70 individual VOCs were identified in the leachate plume of a closed municipal landfill. Concentrations were low when compared with data published for other landfills, and total VOCs accounted for less than 0.1% of the total dissolved organic carbon. The VOC concentrations in the core of the anoxic leachate plume are variable, but in all cases they were found to be near or below detection limits within 200 m of the landfill. In contrast to the VOCs, the distributions of chloride ion, a conservative tracer, and nonvolatile dissolved organic carbon, indicate little dilution over the same distance. Thus, natural attenuation processes are effectively limiting migration of the VOC plume. The distribution of C2-3-benzenes, paired on the basis of their octanol-water partition coefficients and Henry's law constants, were systematically evaluated to assess the relative importance of volatilization, sorption, and biodegradation as attenuation mechanisms. Based on our data, biodegradation appears to be the process primarily responsible for the observed attenuation of VOCs at this site. We believe that the alkylbenzenes are powerful process probes that can and should be exploited in studies of natural attenuation in contaminated ground water systems.

Biodegradation, Environmental↗

PubMed2002

Direct analysis of volatile organic compounds in human breath using a miniaturized cylindrical ion trap mass spectrometer with a membrane inlet.

Membrane introduction mass spectrometry (MIMS) coupled to a miniature mass spectrometer equipped with a cylindrical ion trap (CIT) analyzer was used to monitor the flavor components, 3-phenyl-2-propenal and methyl salicylate, found in cinnamon and wintergreen candies, respectively, directly from human breath. The poly(dimethylsiloxane) (PDMS) membrane was operated in a trap-and-release mode, where the temperature of the membrane was cycled during the experiments, which permitted temporal resolution of the two compounds of interest, facilitating their observation in the complex sample. Under these thermally driven conditions, the 10-90% rise times for both compounds are similar (15 s for methyl salicylate, 17 s for 3-phenyl-2-propenal), but the difference in diffusivity means that the signal for 3-phenyl-2-propenal is delayed and the 10% point occurs 6 s later than that for wintergreen. Additional specificity needed for complex samples was gained by using tandem mass spectrometry.

Acrolein↗

PubMed1992

Human activities as sources of volatile organic compounds in residential environments.

The objectives of the present work were to investigate techniques for the continuous, qualitative monitoring of VOCs and to see how VOC levels were influenced by normal household activities. Three different methods were investigated to measure the VOC levels: infrared spectroscopy, photoionization detection, and gas chromatographic analysis of absorbent tube samples. Results were presented that related changes in levels of VOCs to various human activities commonly occurring in residences, and data were presented that indicated activities such as cooking, arts and crafts, cleaning floors, and painting contributed to short-term increases in VOC levels. VOC levels were diminished by turning on the air conditioner. Results on the effect of humidity on VOCs, both in homes and controlled chambers, were reported.

Air Conditioning↗

PubMed1977

Gas chromatographic-mass spectrometric determination of volatile organic compounds in an urban atmosphere.

Polysorbimide and carbochrome, new sorbents with high temperature stability, have been used to concentrate trace amounts of atmospheric pollutants, and 136 C1-C13 organic compounds, including 126 hydrocarbons, 6 oxygen derivatives and 3 chlorides, were identified in air samples collected in the streets of Leningrad. One of the major features of the composition of the organic constituents of the urban air sampled is the presence of a number of CnH2n hydrocarbons (mainly olefins), and also CnH2n-2 and CnH2n-4 unsaturated hydrocarbons (including alpha-pinene and camphene). A comparison of the results with those of similar studies carried out on air samples from Zürich, Houston and Paris is of considerable interest in connection with the possible effect of geographical factors on the composition and lifetime of organic pollutants in the atmosphere.

Air Pollutants↗

PubMed2002

Remove volatile organic compounds (VOCs) with membrane separation techniques.

Membrane separation, a new technology for removing VOCs including pervaporation, vapor permeation, membrane contactor, and membrane bioreactor was presented. Comparing with traditional techniques, these special techniques are an efficient and energy-saving technology. Vapor permeation can be applied to recovery of organic solvents from exhaust streams. Membrane contactor could be used for removing or recovering VOCs from air or wastewater. Pervaporation and vapor permeation are viable methods for removing VOCs from wastewater to yield a VOC concentrate which could either be destroyed by conventional means, or be recycled for reuse.

Bioreactors↗

PubMed1994

A breath sampling device for measuring human exposure to volatile organic compounds in microgravity.

A compact device for the collection of alveolar air (breath) from humans aboard spacecraft was developed. The system uses silicone one-way valves that operate independent of gravity, and provide minimal backpressure. Small charcoal filters clean ambient air used for inhalation. The device provided good recoveries of organic compounds at the 20 ng/L level, with generally low carryover of these compounds to a blank sample following a sample at exposure to 100 ng/L. When water accumulated in the system, this carryover increased for highly water soluble compounds. The new device was used in parallel with a larger, previously developed alveolar air sampler that requires gravity for proper operation; comparable results were obtained with the two units. The device measures 47 x 34 x 11.4 cm and weighs approximately 3.2 kg. Sufficient space is available within the case to accommodate a number of sample collection options.

Aerospace Medicine↗

PubMedDate not supplied

Efficacy of volatile organic compounds in evoking nasal pungency and odor.

Sensory irritation (pungency) figures prominently among the symptoms associated with polluted indoor environments. In order to separate the pungent from the olfactory response, we measured nasal pungency thresholds in subjects lacking olfaction (anosmics) and odor thresholds in normal controls (normosmics) for a homologous series of ketones and for selected secondary and tertiary alcohols and acetates. As seen previously for homologous alcohols and acetates, both types of nasal thresholds decreased with increasing carbon chain length. Pungency thresholds decreased exponentially with chain length. With respect to all nonreactive chemicals studied so far, threshold nasal pungency is achieved at a fairly constant percentage of vapor saturation, irrespective of molecular size or chemical functional group. Such a relationship does not hold for odor thresholds. The outcome for pungency implies an important role for a physical, rather than chemical, interaction with nasal mucosa.

Acetates↗

PubMed2005

In-needle extraction device designed for gas chromatographic analysis of volatile organic compounds.

A novel in-needle extraction device has been developed for the preconcentration of gaseous organic compounds prior to the determination in gas chromatography (GC). As the extraction medium, a copolymer of methacrylic acid and ethylene glycol dimethacrylate was synthesized. Based on the results in the preliminary experiments, the desorption conditions such as desorption temperature and time have been optimized along with the evaluation of the extraction efficiency. The storage performance of the needle extraction device was also studied. The results clearly demonstrated the excellent extraction performance for typical organic solvents and also suggested the future possibility such as in the applications for the analysis of working environments.

Chromatography, Gas↗

PubMed1999

[Preparation of standard mixture of volatile organic compounds].

This article presented a simple, convenient and flexible device for the preparation of standard mixtures of VOCs. By the aid of a constant pressure on the surface of a liquid with specific composition of VOCs, the liquid passed through a long capillary tube at a definite flow rate. A standard VOCs source was thus formed. The mean relative standard deviation (RSD) of flow rate was 3%. As the outlet of capillary tube inserted in a stream of zero air, the components of liquid vaporized and eventually became a homogeneous gas mixture. The concentration of VOCs in the mixture varied with the pressure applied and the flow rate of dilution air. The mean RSD of concentration of total VOCs in the standard mixture determined by GC method was 5.7%, and the absolute error was 8%. No significient difference was found between the determined and calculated concentrations of the mixture. This method is suitable for preparation of standard mixtures of VOCs with boiling points lower than 150 degrees C.

Air Pollutants↗

PubMed1994

An exposure system for the calibration of passive samplers to volatile organic compounds at low (ppbv) concentrations.

A recycling exposure system, which has characteristics of dynamic and static systems, has been designed and constructed for calibrating passive sampling tubes. This system is very easy to set up and maintain. Organic vapors inside the system are generated by syringe injection, and homogeneous vapors are circulated by a metal-bellows pump. The concentrations of light hydrocarbons (e.g., isoprene) may decrease slightly after circulating for longer than 10 hours; however, this system is very stable for C5-C8 hydrocarbons for at least eight hours. The system has been used successfully to calibrate Perkin-Elmer diffusion tubes packed with Chromosorb 106 for collecting benzene vapor at low exposure doses (< 70 ppmv x min). The entire system can be easily and effectively cleaned by circulating through a U-tube packed with activated carbon.

Air Pollutants↗

PubMed2005

Incinerating volatile organic compounds with ferrospinel catalyst MnFe2O4: an example with isopropyl alcohol.

This paper concerns the incineration of isopropyl alcohol (IPA) using the ferrospinel catalyst MnFe2O4. It covers the preparation of the ferrospinel catalyst, the screening of catalytic activity, catalytic incineration testing, and 72-hr decay testing of the catalyst. The experimental results of catalyst screening reveal that the Mn/Fe catalyst is the best of five prepared catalysts (chromium/iron [Cr/Fe], manganese/iron [Mn/Fe], zinc/iron [Zn/Fe], nickel/iron [Ni/Fe], and pure magnetite [Fe3O4]). In tests of the catalytic incineration system used to convert IPA, 98% conversion was obtained at a space velocity of 24,000 hr(-1), an oxygen (O2) content of 21%, 1700 ppm of IPA, and a reaction temperature of 200 degrees C.

2-Propanol↗

PubMed2000

Volatile organic compounds in indoor environments in Mumbai, India.

Air samples, representing different types of indoor environments, were collected and analyzed for eight hydrocarbons namely, n-hexane, benzene, heptane, toluene, p- and o-xylene, ethyl benzene and n-decane using a cryogenic preconcentration system and a gas chromatograph with a flame-ionization detector. Simultaneous outdoor samples were also collected to determine indoor to outdoor (I/O) ratios for every compound at each location. In all, seven different types of indoor environments were investigated for VOC levels. Toluene concentration levels were found to be high in a hall which was recently renovated. The indoor environment of a kitchen in which a kerosene stove was used and smoker's rooms showed high levels of benzene. The concentrations of VOCs during painting were found to be high and the levels of VOCs depended on the type of paint used. The study revealed that the indoor concentrations of selected VOCs on occasions could be significantly high due to various sources. The data presented here can be useful in developing air quality standards for indoor air.

Air↗