Nonpolar Volatile Organic Compounds Research Articles

Novel family of multi-layer cartridges filled with a new carbon adsorbent for the quantitative determination of volatile organic compounds in the atmosphere

The ability of a new graphitized carbon black adsorbent (Carbograph 5) to retain volatile organic compounds (VOCs) in air has been investigated through laboratory experiments performed by frontal chromatography. An artificial mixture containing 19 different compounds from C 1 to C 7 at levels of 50 ppb (v/v) each was used as eluent. The amounts of VOCs retained by Carbograph 5 were determined by high-resolution GC–flame ionization detection after thermal desorption at 250°C. The retention features of this adsorbent were compared with those provided by Carbograph 1 and Carbograph 2, two graphitic carbons equivalent in specific surface area and adsorption properties to Carbopack B and Carbopack C, respectively. It was found that Carbograph 5 exhibits safe sampling volumes of VOCs much higher than those of Carbograph 1 and is the only hydrophobic material providing performances comparable to those of some molecular sieve adsorbents. Results obtained indicate that Carbograph 5 can be used alone or in combination with other materials. When combined with lighter adsorbents, it allows the quantitative collection of polar and non-polar VOCs with carbon number higher than 3 in air volumes larger than 5 l at any relative humidity. In combination with stronger carbon molecular sieve adsorbents, it makes possible the quantitative collection of components with volatilities ranging from C 2 to C 7 in small samples.

Analysis of Volatile Organic Compounds in Water and Soil Samples by Purge-and-Membrane Mass Spectrometry

A new method, purge-and-membrane mass spectrometry (PAM MS), is introduced for the analysis of volatile organic compounds (VOCs) in water and soil samples. In this method, VOCs are purged from water or soil samples with an inert gas and the stream is directed through a sheet membrane module. The VOCs pervaporate through the membrane directly into the ion source of a mass spectrometer. The limits of detection for nonpolar VOCs such as halogenated hydrocarbons, benzene, toluene, and xylenes were below micrograms per liter in water samples and at low micrograms per kilogram levels in soil samples. The correlation coefficients measured for the compounds studied were typically better than 0.9999 and 0.9975 in water and soil samples, respectively. The relative standard deviations were between 0.5 and 2.0% with water samples and between 4.8 and 14.0% with soil samples. These results demonstrate excellent linearity and repeatability. PAM MS thus provides a highly sensitive, selective, accurate, solvent-free, and rapid analytical method. Tens of samples can be analyzed reliably within 1 h.

Sorption of volatile organic compounds to particles from a combustion source at different temperatures and relative humidities

Sorption of polar and non-polar volatile organic compounds to particles from a combustion source has been measured at different temperatures and relative humidities in laboratory experiments. The soot particles collected from oil furnaces contained 60% (w/w) iron sulfate and 9% (w/w) carbon comparable to the chemical composition of aerosol particles. Sorption experiments were conducted with the unmodified original soot as well as with a water-extracted subsample. A decrease in the sorption with increasing relative humidity was observed for all VOCs on both sorbents. Sorption enthalpies calculated from the measured temperature dependence of the sorption coefficients suggested stronger sorption for polar compared to non-polar compounds of comparable volatility. VOC sorption coefficients normalized to the surface area of the soot were greater than have been previously reported for mineral surfaces. A comparison of sorption coefficients with field data for gas-particle partitioning indicated good agreement on the basis of a log K p,s vs log p L 0 relationship.

“Vapochromic” Compounds as Environmental Sensors. 2. Synthesis and Near-Infrared and Infrared Spectroscopy Studies of [Pt(arylisocyanide)4][Pt(CN)4] upon Exposure to Volatile Organic Compound Vapors

The synthesis, characterization, and vis−NIR−IR vapochromic/spectroscopic studies are reported for isocyanide compounds of the form [Pt(arylisocyanide)4][Pt(CN)4] (where arylisocyanide = p-CNC6H4CnH2n+1; n = 1, 6, 10, 12, 14). The dark blue, solid materials change color in the NIR (near-infrared) spectral region upon exposure to the ambient room-temperature vapor pressure of volatile organic compounds (VOCs). At room temperature the PtPt compounds exhibit strong solid-state absorption and emission bands in the NIR region of the spectrum that are red-shifted from similar bands in the PtPd analogues; (n = 1, λmax abs = 744, λmax emit = 958; n = 6, λmax abs = 841, λmax emit = 910; n = 10, λmax abs = 746, λmax emit = 944; n = 12, λmax abs = 764, λmax emit = 912; n = 14, λmax abs = 690, λmax emit = 876 nm). The positions of these broad bands depend on the number of carbons in the alkyl substituent. The absorption and emission bands for the solid material (n = 10 compound) also exhibit a substantial red-shift upon cooling to 77 K (λmax abs (293 K) = 746; λmax emit (293 K) = 944; λmax abs (77 K) = 846; λmax emit (77 K) = 1094 nm) that is consistent with an alternating cation−anion stacked structure. Qualitatively, compounds with n > 6 respond well to nonpolar VOCs; the n = 1, 6 compounds respond better to polar VOCs. The shifts observed for λmax abs (at 293 K) are on the order of 700 cm-1 and are 2−3 times greater than those exhibited by the PtPd analogue compounds under identical conditions. The n = 10 compound is the most responsive; the positions of the vis−NIR band in the presence of several solvent vapors are as follows: none, 746 nm; methanol, 757; ethanol, 782; 2-propanol, 782; diethyl ether, 787; acetonitrile, 809; hexanes, 775; acetone, 800; benzene, 801; dichloromethane, 811; chloroform, 837. No response was observed for water vapor. IR studies of films of the n = 10 compound on an ATR crystal show that the sorption of VOC by the solid causes no change in the ν(CN) isocyanide stretching frequency but in some cases a substantial shift (0−15 cm-1) in ν(CN) of the cyanide stretch is observed. When the n = 10 compound contacts VOCs capable of H-bonding with the Pt(CN)42- anion, two cyanide stretches are observed. All the spectroscopic data suggest that the VOC penetrates the solid and interacts with the linear chain chromophore to cause the spectral shifts in the vis−NIR−IR spectral regions. The vapochromic shifts are suggested to be due to dipole−dipole and/or H-bonding interactions between the Pt(CN)42- anion and polar VOCs. For nonpolar VOCs, lypophilic interactions between the VOC and the isocyanide ligands that cause no change in the ν(CN) stretching region must cause the NIR vapochromism observed. The absence of a vapochromic response for water vapor is suggested to arise from hydrophobic blocking of the water at the solid/gas interface.

Technique for monitoring ozone precursor hydrocarbons in air at photochemical assessment monitoring stations: Sorbent preconcentration, closed-cycle cooler cryofocusing, and GC-FID analysis

An automated gas chromatograph (autoGC) system that may be used to collect and analyze both polar and nonpolar volatile organic compounds in ambient air has been evaluated. This system combines the use of dual multiadsorbent traps for sampling 57 min h −1 at ambient temperature, a dry helium purge to remove residual water from the sorbents, thermal desorption of analytes onto a Stirling-cooled trap for refocusing, and GC-flame ionization detection (FID). Method detection limits (MDLs), linearity, cleanliness, precision, and accuracy of the autoGC were determined for a set of 57 ozone precursor hydrocarbons. For most of the compounds tested, MDLs were less than 0.40 ppbv, the FID response was linear over the 5–40-ppbv range, and the trap-to-trap precision was ± 10%. This autoGC was found to be a reliable system that would be suitable for use in field sites such as the Photochemical Assessment Monitoring Stations network, which is being implemented in the United States of America.

A full evaporation headspace technique with capillary GC and ITD: a means for quantitating volatile organic compounds in biological samples.

The full evaporation technique (FET), which is a variant of headspace analysis used to overcome matrix effects, was combined with capillary gas chromatography (GC) and ion-trap detection (ITD). The aim was to enable quantitative tests of volatile organic compounds (VOCs) in blood and postmortem tissue samples. FET was applied to sample sized less than 35 mg whose VOCs were released from the matrix at an equilibration temperature of 130 degrees C. A capillary column with a nonpolar stationary phase was used for GC, and ITD was performed with the mass spectrometer run in full-scan mode. The potential of FET-GC-ITD was studied for the analysis of blood samples spiked with low concentrations of ethanol, acetone, 2-propanol, and 2-butanone and on brain tissue that contained methyl tert-butyl ether (MTBE), Benzene, toluene, ethylbenzene, o-, m-, and p-xylene, and propylbenzene. Samples were obtained from the bodies of victims who had inhaled smoke during an arson or accidental fire. There was a linear relationship between peak area and sample size, which indicates that the conditions of full evaporation were met and that the matrix effect was negated. The total analyte amount in the test sample at the limit of quantitation was in the range of 0.4-1 nmol for polar VOCs in blood and 0.03-0.1 nmol for nonpolar VOCs in brain tissue. Data on precision and accuracy of the method are reported.

Occurrence of Oxygenated Volatile Organic Compounds (VOC) in Antarctica

Polar and non-polar VOC present in six different sites located near Terra Nova Bay in Antarctica were determined by HRGC-MS. 76 different components were positively identified. Among them, particularly important are oxygenated components (free acids, aldehydes, ketones, alcohols, esters, ethers and furanes) as they account for the largest portion of the organic fraction. Biogenic emission seem to be the major source for many of them. This would explain their ubiquitous occurrence in the troposphere.

Sorbent-Based Method for the Analysis of Ambient Air Using Supercritical Fluid Desorption/Gas Chromatography

Abstract The work described in this paper shows how we have investigated the utility of polar polyimide sorbents for the collection of polar and non-polar volatile organic compounds in ambient air. The results indicate that supercritical carbon dioxide can be used to recover a variety of compounds with a wide range of volatilities from polyimide sorbents and that these compounds can be effectively collected onto an adsorbent micro-trap after the expansion of the fluid prior to thermal desorption gas chromatographic analysis. Molecular sieve 3A was used and found to have a very high capacity for removal of water from the supercritical fluid extract stream. The sieve tended to adsorb polar compounds in the absence of water; the presence of water sometimes reduced analyte adsorption. The method was used to collect, recover, and analyze volatile organic compounds from the air of a laboratory building and was shown to be quite sensitive for appropriate compounds.

Transfer of volatile substances from water to the atmosphere

Mass transfer coefficients and the degree of saturation of the exit gas are important parameters in transferring volatile organic substances from water to the atmosphere. Aeration systems in batch and continuous flow reactors are discussed based on theoretical analysis and experimental data. Three different ranges of the degree of saturation of the exit gas are introduced and their significance for model experiments and technical operations is evaluated. The effect of the aeration system and of surface active agents on the mass transfer coefficient of tetrachloroethylene is studied. Mass transfer coefficients for six nonpolar volatile organic compounds are presented. The stripping efficiencies of different types of gas-liquid contact devices used in water and waste water treatment are assessed.