Semivolatile compounds

Dynamic headspace GC/MS. The distillation of volatile and semivolatile compounds into a continuously flowing stream of carrier gas and into a device for trapping sample components. Contents of the trap are then introduced onto a gas chromatographic column. This is followed by mass spectrometric analysis of compounds eluting from the gas chromatograph. 

SW-846, is used to measure emissions of semivolatile principal organic constituents. Method 0010 is designed to determine destruction and removal efficiency (DRE) of POHCs from incineration systems. The method involves a modification of the EPA Method 5 sampling train and may be used to determine particulate emission rates from stationary sources. The method is applied to semivolatile compounds, including polychlorinated biphenyls (PCBs), chlorinated dibenzodioxins and dibenzofurans, polycyclic organic matter, and other semivolatile organic compounds. 

Prepai ative isolation of nonvolatile and semivolatile organic compounds fractions (hydrophobic weak acids, hydrophobic weak bases, hydrophobic neutrals, humic and fulvic acids) from natural and drinking waters in optimal conditions was systematically investigated by solid-phase extraction method with porous polymer sorbents followed by isolation from general concentrate of antropogenic and/or toxic semivolatile compounds produced in chlorination and ozonation processes. 

Conessa, J.A., FuUena, A., and Font, R., Tire pyrolysis Evolution of volatile and semivolatile compounds, Energy Fuel, 14, 409, 2000. 

Volatile and semivolatile compounds are present in honeys and are attributed to aroma qualities. Aroma compoimds can indicate floral and geographical origins and processing treatments. Aroma compounds come from nectar or honeydew. Aroma components can be also formed during fhermal processing and sforage (Bonvehi and Coll, 2003 Soria et ah, 2003). More than 400 components have been detected in the volatile flavor fraction of honey... 

Raising the temperature of the soil increases the vapor pressure of the contaminants, improving their ability to volatilize. Many semivolatile compounds will eventually be released as the temperature rises, although these compounds tend to need longer residence times. 

U.S. Environmental Protection Agency (USEPA). 1994. Semivolatile Compounds in the General U.S. Population NHATS FY86 Results. Vols. I and II. U.S. Environ. Protection Agen. Rep. EPA 747-R-94-001. 409 pp. 

An ELSD converts the HPLC eluent into a particle stream and measures the scattered radiation. It offers universal detection for nonvolatile or semivolatile compounds and has higher sensitivity than the RI detector (in the low ng range) in addition to being compatible with gradient analysis. ELSD is routinely used in combinatorial screening. Response factors are less variable than that of other detectors. An ELSD consists of a nebulizer equipped with a constant temperature drift tube where a counter-current of heated air or nitrogen reduces the HPLC eluent into a fine stream of analyte particles. A laser or a polychromatic beam intersects the particle stream, and the scattered radiation is amplified by a photomultiplier. Manufacturers include Alltech, Polymer Laboratories, Shimadzu, Waters, Sedere, and ESA. 

Accelerated solvent extraction is a new technique for the extraction of a range of organic pollutants from soils and related material. The technique is based on the use of a solvent or combination of solvents to extract organic pollutants at elevated pressure and temperature from a solid matrix. The range of organic pollutants for which the technique is proposed includes semivolatile compounds, organochlorine pesticides, organophosphorus pesticides, chlorinated herbicides, polychlorinated biphenyls and polycyclic aromatic hydrocarbons [53-56],... 

The second class of organic compounds, the semivolatile compounds, typically have high boiling points, or high boiling ranges, and are not always easily detected... 

Soxhlet extraction (EPA SW-846 3540) is a very efficient extraction process that is commonly used for semivolatile petroleum constituents. In the method, the solvent is heated and refluxed (recirculated) through the soil sample continuously for 16 hours, or overnight. This method generates a relatively large volume of extract that needs to be concentrated. Thus, it is more appropriate for semivolatile constituents than for volatile constituents. Sonication extraction (EPA SW-846 3550) can also be used for semivolatile compounds, and as the name suggests, involves the use of sound waves to enhance analyte transfer from sample to solvent. Sonication is a faster technique than Soxhlet extraction and can require less solvent. 

The most common method for GC/MS analysis of semivolatile compounds (EPA SW-846 8270) includes 16 polycyclic aromatic compounds, some of which commonly occur in middle distillate to heavy petroleum products. The method also quantifies phenols and cresols, compounds that are not hydrocarbons but may occur in petroleum products. Phenols and cresols are more likely found in crude oils and weathered petroleum products. 

Arthur and Pawliszyn introduced solid-phase microextraction (SPME) in 1990 as a solvent-free sampling technique that reduces the steps of extraction, cleanup, and concentration to a unique step. SPME utilizes a small segment of fused-silica fiber coated with a polymeric phase to extract the analytes from the sample and to introduce them into a chromatographic system. Initially, SPME was used to analyze pollutants in water - via direct extraction. Subsequently, SPME was applied to more complex matrixes, such as solid samples or biological fluids. With these types of samples, direct SPME is not recommended nevertheless, the headspace mode (HSSPME) is an effective alternative to extracting volatile and semivolatile compounds from complex matrixes. (Adapted from Llompart et ah, 2001)... 

The process has limited application for soils contaminated with polychlorinated biphenyls or any other dioxin precursor. Semivolatile compounds with boiling points greater than 800°F cannot be effectively removed from the soil in a one-pass treatment. The soil characteristic that most affects treatment is moisture content. All information in this summary is based on information provided by the vendor and has not been independently verified. 

The vendor claims that the TDR process can be used to treat soil and sludge contaminated with polychlorinated biphenyls, polynuclear aromatic compounds, solvents, dioxins, furans, organic pesticides and herbicides, solvents, petroleum wastes, as well as nonhalogenated volatile and semivolatile compounds. The treated residuals from the process include recovered water, oil that can be used for recycling as an alternative fuel or for recycling or can be disposed, and clean soil that can be used as backfill. The volume of treated sludge is reduced by as much as 95% by this thermal process, depending on the initial level of contaminants. 

Because it is a nonselective treatment, chemical oxidation is best suited for media with low concentrations of contaminants. This technology has been demonstrated to be effective in treating wastes contaminated with halogenated and nonhalogenated volatile and semivolatile compounds, polychlorinated biphenyls (PCBs), pesticides, cyanides, and volatile and nonvolatile metals. 

BioSparge is typically ineffective in silts and clays where the porosity and permeability are low. Also, remediation of certain semivolatile compounds, including chlorinated solvents, requires that the system be modified by the addition of an ozone generator. The ozone reacts with the chlorinated compounds to produce by-products that can be biodegraded. 

According to the vendor, the in situ bioremediation treatment system is applicable to soils contaminated with volatile organic compounds (VOCs) and semivolatile compounds, including those comprising various fuels, hydrocarbons, and solvents. The use of methane as an easily oxidized co-metabolite makes the technology amenable to treating soils contaminated with halogenated hydrocarbons. 

All solvent extraction technologies use flammable organic extraction fluids that present potential fire and explosion hazards. Several of the extraction fluids include volatile or semivolatile compounds, which can create explosive vapor mixtures. A number of the extraction fluids contain toxic organic compounds therefore, process designs must minimize or eliminate personnel exposure to these compounds. 

Atrazine, however, would be a nonvolatile compound - 1/(HKg)>> /Kl -because equilibrium is strongly to the liquid phase due to the small Henry s law constant. There is also a strong gas phase resistance to the transfer. Atrazine was manufactured to remain in the hquid phase, where it will act as a herbicide, rather than in the gas phase, where farm personnel will be breathing this toxic chemical. If you were going to pick a compound that is not made by humans from the list of those that are a gas or liquid in our environment, a good guess is that it would be a volatile or semivolatile compound. There are only a few nonionic environmental compounds that are nonvolatile. Remarkably, one of them is water. While the atmosphere may be as much as 3 % water, the water bodies in the world are very close to 100% water. The equilibrium is strongly to the hquid side because of the small Henry s law constant. 

Consider Example 8.5, except with (a) toluene (a volatile compound) and (b) trichloromethane (a semivolatile compound) added to the water, instead of toxaphene. Sketch the concentration profiles that would be expected at some point in time. 

It is important to note, however (see later), that it is not necessary that the gas-phase concentration exceed the saturation vapor pressure for an organic to exist in particles. Thus, partitioning into the organic phase of existing particles can occur at lower gas-phase concentrations (see Section D on gas-particle pardoning of semivolatile compounds). However, even in this case it is necessary that the organic not be highly volatile for this to occur. 

In short, differentiating between adsorption on a solid and absorption into a liquid for partitioning of semivolatile compounds in the atmosphere is often difficult to do in an unambiguous manner. However, the use of a combination of approaches can help to differentiate these two mechanisms and, perhaps more important, give some insight into the mechanisms of interaction of the SOC with the condensed-phase material. 

The release of semivolatile compounds from a variety of nitrogen containing polymers, including ABS, PA 6 PU and melamine/urea formaldehyde resins can be found in the literature (52). The temperature of treatment runs from 70°C to 300°C, i.e., low temperature pyrolysis, if pyrolysis at all. 

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