Volatile compounds organics, extraction from

The volatile substances were extracted from portions of 0. lg hair using solid-phase micro extraction (SPME). The method uses a fibre coated with an adsorbent that can extract organic compounds from the headspace above the sample. Extracted compounds are desorbed upon exposure of the SPME fibre in the heated injector port of a gas chromatograph (GC). 

In sorbent tube sampling (Figure 3.5), volatile and semi-volatile compounds are pumped from the air and trapped on the surface of the sorbent. By sampling a measured quantity of air (typical volumes of 10-500 m3), quantitative sampling is possible. The sorbent tube is then sealed and transported back to the laboratory for analysis. Desorption of volatile and semi-volatile compounds takes place either by the use of organic solvents (solvent extraction) or heat (thermal desorption), followed by analysis using gas chromatography (see later). 

Thermal desorption (TD) is a technique in which solid or semisolid samples are heated under a flow of inert gas. Volatile and semivolatile organic compounds are extracted from the sample matrix into the gas stream and introduced into a gas chromatograph. Samples are typically weighed into a replaceable FIFE tube liner, which is inserted into a stainless steel tube for heating. 

Analysis of plants normally involves a sample preparation stage such as extraction or distillation followed by analysis with gas chromatography or liquid chromatography. The common methods used currently for the isolation of essential oils from natural products are steam distillation and solvent extraction (Ozel Kaymaz, 2004). Losses of some volatile compounds, low extraction efficiency, degradation of xmsaturated compounds through thermal or hydrolytic effects, and toxic solvent residue in the extract may be encountered with these extraction methods. Recently, more efficient extraction methods, such as supercritical fluid extraction (SFE) (Simandi et al., 1998) and accelerated solvent extraction (ASE) (Schafer, 1998) have been used for the isolation of organic compounds from various plants. Subcritical or superheated water extraction (SWE) is non-toxic, readily available, cheap, safe, non-flammable and is a recyclable option. 

Workstations and robotic systems are very expensive, so inexpensive alternatives such as flow configurations have been developed for automated sample preparation. The earliest flow systems for sample preparation were used for GC determination (with flame ionization detector [FID] or electron capture detector [EGD] detection) of organic compounds, which requires no special extraction or derivatization, in environmental matrices [30-34]. Automated GC-MS systems for the determination of volatiles in water or air [35-38] are the most commonly reported. Detailed descriptions of these systems can be found elsewhere in this book. Few continuous flow systems (CFSs) for the automated pretreatment of biological fluids in combination with GC-MS have been developed to date. The intrinsically discrete nature of the GC-MS sample introduction mechanism makes online coupling to continuous flow systems theoretically incompatible for reasons such as the different types of fluids used (liquid and gas) and the fact that the chromatographic column affords volumes of only 1 to 2 j,l of cleaned-up extract. Therefore, the organic extracts from CFSs have traditionally been collected in glass vials and aliquots for manual transfer to the GC-MS instrument (off-line approach) only in a few cases is an appropriate interface used to link the CFS to the GC-MS instrument (on-line approach). These are the topics dealt with below. 

To satisfy the Resource Conservation and Recovery Act (1977) and its amendment for hazardous and solid waste (1984), the 80(K) Series Methods have been designed to analyze solid waste, soUs, and groundwater. In particular, methods 8240/8260 require the use of a purge-and-trap device in conjunction with packed or capillary GC/MS, respectively, for the analysis of purgeable organic compounds. Methods 8250/8270 concern analyses for the less-volatile bases, neutrals, and acids by GC/MS after extraction from the matrix by an organic solvent. 

Base, neutral, and acid compounds, which may be less volatile, are extracted from the matrix with organic solvents. 

The study of biochemical natural products has also been aided through the application of two-dimensional GC. In many studies, it has been observed that volatile organic compounds from plants (for example, in fruits) show species-specific distributions in chiral abundances. Observations have shown that related species produce similar compounds, but at differing ratios, and the study of such distributions yields information on speciation and plant genetics. In particular, the determination of hydroxyl fatty acid adducts produced from bacterial processes has been a successful application. In the reported applications, enantiomeric determination of polyhydroxyl alkanoic acids extracted from intracellular regions has been enabled (45). 

Soil vapor extraction (SVE) is a relatively new yet widely applied technology for the remediation of soils contaminated with volatile organic compounds (VOC) in the unsaturated zone above the water table (vadose zone). The process consists of generating an airstream through the contaminated soil subsurface in order to enhance the volatilization of organic contaminants and thus remove them from the soil matrix.913... 

SPME can be used to extract organic compounds from a solid matrix as long as target compounds can be released from the matrix into the headspace. For volatile compounds, the release of analytes into the headspace is relatively easy because analytes tend to vaporise once they are dissociated from their matrix. For semi-volatile compounds, the... 

The mechanisms for the NMHCs (except DMS) required to fully characterise OH chemistry were extracted from a recently updated version of the Master Chemical Mechanism (MCM 3.0, available at http //mcm.leeds.ac.uk/MCM/). The MCM treats the degradation of 125 volatile organic compounds (VOCs) and considers oxidation by OH, NO3, and O3, as well as the chemistry of the subsequent oxidation products. These steps continue until CO2 and H2O are formed as final products of the oxidation. The MCM has been constructed using chemical kinetics data (rate coefficients, branching ratios, reaction products, absorption cross sections and quantum yields) taken from several recent evaluations and reviews or estimated according to the MCM protocol (Jenkin et al., 1997, 2003 Saunders et al., 2003). The MCM is an explicit mechanism and, as such, does not suffer from the limitations of a lumped scheme or one containing surrogate species to represent the chemistry of many species. 

Tarsal, metatarsal, caudal, interdigital and preorbital glandular structures have been described in the black-tailed deer, Odocoileus hemionus columbianus. The tarsal organ received considerable attention from chemists and behavioral scientists during the early years of chemical research on mammalian semiochemicals. The major constituent of the complex mixture of volatile compounds associated with the tarsal hair tuft of this mule deer, (Z)-6-dodecen-4-olide [ 125], was subsequently found to be a mixture of the R and S enantiomers in a ratio of 89 11 respectively [ 126]. It was later found that this compound does not originate in the tarsal structure itself, but that it is extracted from the animal s urine by the tarsal hair tuft, which is specially adapted to extract lipids from urine [127]. 

As regards a contaminated soil, this type of analysis may not be possible because the various hydrocarbons cannot be extracted from the sample with equal efficiency. Volatile organic compounds require special procedures to achieve satisfactory recovery from the soil matrix. It thus becomes important to distinguish between those compounds that are considered to be volatile and those that rank as semi- or nonvolatile compounds. 

A method was developed and tested for collecting semi- and non-volatile brominated organic compounds from air using a glass fiber filter and a high-volume air sampler. Exposed filters were extracted with acetone and the extracts analyzed by either glc/ms/comp, glc/ecd or tic. Recoveries of selected compounds from the filter material were >87%. 

King, Buck Technologies, Inc. s, MultiMode combustion (MMC) system treats volatile organic compound (VOC) emissions from soil vapor extraction (SVE) operations. The sequential operation of a thermal oxidizer (ThermOx) followed by a catalytic oxidizer (CatOx) is the basic concept of the MMC system. The CatOx technology is discussed in a separate technology summary (T0780). 

Remediation Service, International manufactures internal combustion engine (ICE) systems that are used to destroy volatile organic compounds (VOCs) in contaminated soil. Vapors are extracted from the soil using the vacuum generated by the engine. The vapors are then burned as... 

Due to their extremely polar character, tetracyclines bind with proteins to form conjugates that are difficult to extract from biological matrices. Use of dilute mineral acids is of great help in dissociating tetracyclines from proteins, but once in aqueous solution, their exfraction into volatile organic solvents for further concentration and cleanup is hampered by the unfavorable partition coefficients. Most of these antibiotics are photosensitive compounds, whereas all of them show poor stability under strong acidic and alkaline conditions with reversible formation of the 4-epi-tetracyclines in weakly acidic conditions (pH 3), and anhydro-tetracyclines in strong acidic conditions (below pH 2). 

Nonaqueous Liquid Wastes Protocol. Nonaqueous liquid wastes were defined to include samples that range from water-soluble organic liquids to immiscible oils. Only a limited amount of data are available on the applicability of this protocol (Figure 4) to compounds other than oils or petroleum products. This medium differs from other environmental media because mutagenic materials are often concentrated in organic liquids. Therefore, this protocol incorporates dilution steps rather than the concentration techniques used in the other media protocols. This protocol is also unique because of the opportunity to test neat samples or samples diluted with DMSO rather than sample components isolated with an absorbent or extracted with a solvent. For this reason, samples treated with this protocol should contain polar compounds and/or volatile compounds that would be lost when the other protocols are used. 

---