Monitoring Of Volatile Organic Compounds Research Articles

Trace gas monitoring at the Mauna Loa Baseline Observatory using Proton-Transfer Reaction Mass Spectrometry

Real time monitoring of volatile organic compounds (VOCs) using a Proton-Transfer Reaction Mass Spectrometer was performed at the Mauna Loa Baseline Station (19.54N, 155.58W) in March/April 2001 (March 23, 2001–April 17, 2001). Mixing ratios for methanol, acetone, acetonitrile, isoprene and methyl vinyl ketone (MVK) plus methacrolein (MACR) ranged between 0.2 and 1.8, 0.2 and 1, 0.07 and 0.2, <0.02 and 0.3, and <0.02 and 0.5ppbv, respectively. Biomass burning plumes transported from South-East Asia and the Indian Subcontinent across the Pacific influenced part of the measurement campaign. ΔAcetonitrile/ΔCO and Δacetone/Δacetonitrile ratios in these cases were 1.5×10−3 to 2.5×10−3 and 2–5ppbv/ppbv, respectively. Overall Asian outflow events were not as frequent during Spring 2001 as in previous years. Methanol did not show significant correlation with CO, acetonitrile, and acetone. The abundance of acetone and CO seemed to be influenced but not dominated by biomass burning and domestic biofuel emissions.

The application of proton transfer reaction-mass spectrometry (PTR-MS) to the monitoring and analysis of volatile organic compounds in the atmosphere.

Proton transfer reaction-mass spectrometry (PTR-MS) is a new and emerging technique for the measurement and monitoring of volatile organic compounds (VOCs) at low concentrations in gaseous samples in more-or-less real time. Utilising chemical ionisation, it combines the desirable attributes of high sensitivity and short integration times with good precision and accuracy. Recently it has been exploited in applications related to atmospheric science. Here, the principles of operation of the PTR-MS are described, its advantages and disadvantages discussed, its inherent uncertainties highlighted, some of its uses in atmospheric sciences reviewed, and some suggestions made on its future application to atmospheric chemistry.

Fingerprinting mass spectrometry by PTR-MS: heat treatment vs. pressure treatment of red orange juice—a case study

Proton transfer reaction mass spectrometry (PTR-MS) is more and more applied to rather different fields of research and applications showing interesting performances where high sensitivity and fast monitoring of volatile organic compounds (VOCs) are required. Based on this technique and aiming at the realisation of an automatic system for routine applications in food science and technology, we tested here a novel approach for fingerprinting mass spectrometric detection and analysis of complex mixtures of VOCs. In particular, we describe and discuss corresponding head space (HS) sampling methods and possible data analysis techniques. As a first test case we studied here the properties of four red orange juices processed by different stabilisation methods starting from the same industrial batch: untreated juice, thermal pasteurised (flash and standard) juice and high pressure stabilised juice. We demonstrate the possibility of a fast automatic discrimination/classification of the samples with the further advantage, compared to the use of electronic noses, of useful information on the mass of the discriminating compounds. Moreover, first comparisons with discriminative analysis by a sensory panel shows evidence that there is a correlation between the ability of the PTR-MS to distinguish different juice samples and that of a panel of trained judges with the obvious advantages of an instrumental approach.

Membrane and trap system for continuous monitoring of volatile organic compounds using a portable gas chromatograph with thermal conductivity detector

A device for continuous monitoring of volatile organic compounds by collection of analytes by membrane permeation followed by their concentration on a solid sorbent and injection into a gas chromatograph on thermal desorption is presented. The transfer line between the small trap and the gas chromatograph is a resistance-heated silicosteel capillary column which effects pre-separation or separation of analytes. The device performs automatic injections, is portable because it is powered by a 12-V DC battery, and is light since it incorporates a small carrier gas cylinder and a micro thermal conductivity detector (TCD). Factors affecting the sensitivity of the TCD in the membrane and trap system were evaluated. Separation is performed in less than 30 s for benzene, toluene, trichloroethylene, and tetrachloroethylene, the resolution and peak shapes are very good, and the limits of detection under these experimental conditions were 25 ppt, 30 ppt, 85 ppt, and 90 ppt, respectively. The device was tested for continuous monitoring of thermo-oxidative degradation products of polystyrene.

Stable carbon isotope fractionation during enhanced in situ bioremediation of trichloroethene.

Time-series stable carbon isotope monitoring of volatile organic compounds (VOCs) atthe Idaho National Engineering and Environmental Laboratory's (INEEL) field site Test Area North (TAN) was conducted during a pilot study to investigate the treatment potential of using lactate to stimulate in situ biologic reductive dechlorination of trichloroethene (TCE). The isotope ratios of TCE and its biodegradation byproducts, cis-dichloroethene (c-DCE), trans-dichloroethene (t-DCE), vinyl chloride (VC), and ethene, in groundwater samples collected during the pilot studywere preconcentrated with a combination of purge-and-trap and cryogenic techniques in order to allow for reproducible isotopic measurements of the low concentrations of these compounds in the samples (down to 0.04 microM, or 5 ppb, of TCE). Compound-specific stable isotope monitoring of chlorinated solvents clearly differentiated between the effects of groundwater transport, dissolution of DNAPL at the source, and enhanced bioremediation. Isotope data from all wells within the zone of lactate influence exhibited large kinetic isotope effects during the reduction of c-DCE to VC and VC to ethene. Despite these large effects, the carbon isotope ratio of ethene in all these wells reached the carbon isotope ratios of the initial dissolved TCE, confirming the complete conversion of dissolved TCEto ethene. Conversely, the carbon isotope ratios of t-DCE were only marginally affected during the study, indicating that minimal biologic degradation of t-DCE was occurring.

Isolation and Determination of Volatile Organic Compounds from Water by Dynamic Purge-and-Trap Technique Coupled with Capillary Gas Chromatography

The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water.

Broadly tunable, mode-hop-tuned cw optical parametric oscillator based on periodically poled lithium niobate

We describe a broadly tunable, cw optical parametric oscillator (OPO) based on periodically poled lithium niobate. The OPO can be tuned over a broad region in the mid IR (2900-3100 cm(-1)) covering the important C-H stretch region while a high spectral resolution (<0.1 cm(-1)) is maintained. The OPO is the light source for a field-portable photoacoustic spectrometer for gas-phase monitoring of volatile organic compounds.

On-line analysis of reactive VOCs from urban lawn mowing.

We measured the release of volatile organic compounds (VOCs) resulting from lawn mowing during continuous ambient air measurements in July and August 1998 in the outskirts of Innsbruck, Austria. These measurements were made with a proton-transfer-reaction mass spectrometry system, which allowed simultaneous, on-line monitoring of VOCs in the pptv range. We observed the emission of C6 wound compounds, including (Z)-3-hexenal, (E)-2-hexenal, hexenol plus hexanal, and acetaldehyde immediately following lawn mowing, and a rise in background levels of C6 wound compounds that lasted for several hours. Peak levels of biogenic VOCs following mowing were in the same concentration range (20-60 ppbv) as those originating from combustion engines of lawn mowers, and integrated biogenic emissions were much greater in the drying grass clippings. Additional emissions of acetone and other VOCs resulted from rainfall on these clippings. Since the estimated atmospheric chemical reactivity of VOCs resulting from lawn mowing is of the same order of magnitude as unburned hydrocarbons released during the mowing by gasoline-powered lawn mowers, these biogenic VOCs should be considered in urban air-quality control strategies.

Online Monitoring of Air Quality at the Postanesthetic Care Unit by Proton-Transfer-Reaction Mass Spectrometry

The subthreshold exposure to trace anesthetic gases is not associated with considerable risk of adverse health effects. Online control of ambient air exchange at the postoperative workplace may help in supervising air quality and lead to cost reduction. A proton-transfer-reaction mass spectrometer system was used for online monitoring of volatile organic compounds, especially anesthetic gases. The mean exposure to sevoflurane and isoflurane at the urological postanesthesia care unit (PACU) was 15.9 and 9.5 parts per billion, respectively. Sevoflurane and isoflurane concentrations at the urological PACU showed a patient turnover-dependent burden during our investigation period. Because modern PACUs have a high ventilation capacity, the 24-h occupational burden by anesthetic gases at the PACU is relatively low. Monitoring and controlling of ambient air by automatic built-in alarm systems would be useful for quality control of the postoperative workplace. Moreover, energy costs of ventilation systems could be reduced by coupling ventilation capacity to the effective exposure.

Online monitoring of air quality at the postanesthetic care unit by proton-transfer-reaction mass spectrometry.

The subthreshold exposure to trace anesthetic gases is not associated with considerable risk of adverse health effects. Online control of ambient air exchange at the postoperative workplace may help in supervising air quality and lead to cost reduction. A proton-transfer-reaction mass spectrometer system was used for online monitoring of volatile organic compounds, especially anesthetic gases. The mean exposure to sevoflurane and isoflurane at the urological postanesthesia care unit (PACU) was 15.9 and 9.5 parts per billion, respectively. Sevoflurane and isoflurane concentrations at the urological PACU showed a patient turnover-dependent burden during our investigation period. Because modern PACUs have a high ventilation capacity, the 24-h occupational burden by anesthetic gases at the PACU is relatively low. Monitoring and controlling of ambient air by automatic built-in alarm systems would be useful for quality control of the postoperative workplace. Moreover, energy costs of ventilation systems could be reduced by coupling ventilation capacity to the effective exposure.

Membrane extraction with a sorbent interface for headspace monitoring of aqueous samples using a cap sampling device

A cap-shaped device was employed for headspace sampling. This sampling device coupled to membrane extraction with a sorbent interface (MESI) is intended to perform on-site and on-line aqueous sample monitoring. A laboratory sampling testwas performed both at the water surface and under water, and it showed some advantages in underwater monitoring. A group of volatile organic compounds (VOCs), varying in PDMS/gas and gas/water distribution constants, benzene, toluene, ethylbenzene, o-xylene, and trichloroethylene (TCE), was used for the sampling study. Magnetic stirring of the sample and circulation of the headspace air with a microfan were used for the enhancement of mass transfer between sample matrix and membrane to obtain higher extraction rate and efficiency. The agitation approaches were investigated individually and compared. The results showed that simultaneous agitation in water and air could greatly improve the extraction efficiency. Good linearity and precision and low detection limits were obtained for water-surface monitoring. The study demonstrated that Cap-MESI is a useful tool for field headspace monitoring of volatile organic compounds.

Evaluation of two different direct-sampling ion-trap mass-spectrometry methods for monitoring halocarbon compounds in air

Two different direct-sampling ion-trap mass spectrometry (DSITMS) methods are evaluated for monitoring trace levels of volatile organic compounds (VOCs) in air. The first is based on the use of a sample introduction system that mixes the air sample into a helium stream prior to introduction into the ion trap through an open-split interface. The second utilizes a valve and uses zero air to flush the contents of the sample loop into the ion trap. Unique features of this system are its use of air in place of helium as a buffer gas for the ion trap, and the optimization of experimental parameters to maintain sensitivity and unit mass resolution. Dichlorodifluoromethane (CFC12) and carbon tetrachloride (CCI 4 ) were employed as test compounds for this study. Figures of merit for both sample introduction methods were comparable. Detection limits were approximately 50 parts per billion by volume in MS, selected ion monitoring (SIM), and MS/MS modes. Analysis speeds were on the order of 20 s or less per sample. The sensitivity of the ion trap, inherent selectivity of MS/MS, and fast response times of these sample introduction systems make these DSITMS techniques suitable for many applications that require on-line, real-time monitoring of VOCs in air.

Evaluation of a Passive Sampler for Volatile Organic Compounds at ppb Concentrations, Varying Temperatures, and Humidities with 24-h Exposures. 2. Sampler Performance

The performance of the 3M 3520 organic vapor monitor (OVM) as a tool for monitoring inhalation exposures to volatile organic compounds (VOCs) in nonoccupational community environments was evaluated by using combined controlled test atmospheres of benzene, 1,3-butadiene, carbon tetrachloride, chloroform, 1,4-dichlorobenzene, methylene chloride, styrene, tetrachloroethylene, and toluene. Eight OVMs were simultaneously exposed to concentrations of 10, 20, and 200 μg/m3 in combination with temperatures of 10, 25, and 40 °C and relative humidities of 12, 50, and 90% for 24 h. The results of this study indicate that the performance of the 3520 OVM is compound-specific and depends on concentration, temperature, and humidity. With the exception of 1,3-butadiene under most conditions and styrene and methylene chloride at very high relative humidities, recoveries showed a negative bias as compared to calculated chamber concentrations but were generally within ±25% of theory, indicating that the 3520 OVM can be effectively used over the range of concentrations and environmental conditions tested with a 24-h sampling period. Increasing humidities resulted in increasing negative bias from full recovery. Reverse diffusion experiments conducted at 200 μg/m3 and five temperature/humidity combinations indicated diffusion losses only for 1,3-butadiene, methylene chloride, and styrene under increased humidity conditions. The recovery rates reported in this study can be used for estimating measurement biases when using OVMs for indoor, outdoor, and personal air monitoring of VOCs in community environments.

ChemInform Abstract: Proton‐Transfer‐Reaction Mass Spectrometry (PTR‐MS): On‐Line Monitoring of Volatile Organic Compounds at pptv Levels

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A catalogue of urban hydrocarbons for the city of Leeds: atmospheric monitoring of volatile organic compounds by thermal desorption-gas chromatography.

A method has been developed for the speciation and quantitative determination of hydrocarbons in urban air in the city of Leeds. Hydrocarbons were pre-concentrated by adsorbent tube air sampling and analyzed using thermal desorption and gas chromatography with flame ionization detection and structural confirmation by mass spectrometric detection. While automated volatile organic compound (VOC) analyzers produced data for a maximum of about 30 compounds simultaneously, with the method described here, a total of 68 C6-C12 hydrocarbons were measured simultaneously in one analysis at parts per billion (ppb) levels. Several monitoring surveys were performed, one during the winter of 1993 and the other in the summer of 1994, at a number of sites to investigate the levels of VOCs identified in the urban air of Leeds.

Proton-transfer-reaction mass spectrometry (PTR-MS): on-line monitoring of volatile organic compounds at volume mixingratios of a few pptv

A system for on-line measurements of trace compounds in air with concentrations as low as a few pptv has been developed on the basis of proton transfer reactions. The sensitivity of this system is demonstrated by means of calibration data of benzene and data on the diurnal variation of C9-alkylbenzene and its 13C-isotope in ambient air. First on-line data on the concentrations of volatile organic compounds obtained during plane flights are presented.

Multidimensional capillary gas chromatography for the monitoring of individual non-methane hydrocarbons in air

Mainly of anthropogenic origin, volatile organic compounds (VOCs) are now well known to represent air pollutants of first priority, because of their harmful direct and indirect impacts on human health. So, a permanent and continuously monitoring of individual VOC in the atmosphere and especially in urban air becomes more and more required. In this paper, the ability of the multidimensional gas chromatography to constitute an alternative possibility in the monitoring of individual non-methane hydrocarbons (NMHC) in the atmosphere is demonstrated. The principle of the method as well as of the sampling and analytical system are described. Results obtained from a 2 years monitoring experiment in different areas in Douai are also reported.

Silicone membrane measuring system with SnO 2 gas sensor for on-line monitoring of volatile organic compounds in water

The measuring system combining membrane permeation processes with SnO 2 gas sensor has been tested. Analytes permeation from the water sample into the gas phase via polydimethylsiloxane membrane (0.2 mm) have been studied. Permeation tests have been carried out for selected organic compounds belonging to oxygenated (ethanol, butanol), chlorinated (tetrachloromethane, trichloroethylene) and aromatic hydrocarbons (BTEX: benzene, toluene, ethylbenzene, p-xylene) with different polarity and solubility in water in the form of test water solutions. The influence of an analyte character and its concentration (4–800 ppm), temperature (20–35°C) and ionic strength of the water matrix (by the addition of 0–20% w/v NaCl) on the permeation process has been studied. The SnO 2 sensor has been used as a detector.

Improved detection limit of the proton-transfer reaction mass spectrometer: on-line monitoring of volatile organic compounds at mixing ratios of a few pptv

Improved detection limit of the proton-transfer reaction mass spectrometer: on-line monitoring of volatile organic compounds at mixing ratios of a few pptv

Determination of Volatile Organic Compounds in Groundwater by GC: Comparison Between Headspace and Purge and Trap

Two methods for determining fuel contamination in groundwaters are compared. The first is based on headspace extraction, while the other utilizes purge and trap. Analyses, in both cases, are made by gas chromatography/flame ionization detection, with benzene, toluene, and xylene isomers as monitoring agents for fuel leaks. When compared, results show satisfactory agreement if we take into account the high levels of fuel contamination found in samples collected in control wells from a gas station in an urban site. Thus headspace/gas chromatography can be used, as an alternative technique, to monitoring of volatile organic compounds in groundwater. The main advantages when compared to purge and trap/gas chromatography are simplicity, low cost, and automatic sample handling. When a mass spectrometry detector was used, ethylmethylbenzene and trimethylbenzene isomers were detected in the water samples. These compounds could also be used as alternative tracers for fuel leak detection.