Direct thermal extraction

This overview is focused on the on-line coupling of pressurized liquid extraction (PLE), microwave-assisted extraction (MAE), supercritical fluid extraction (SEE) and sonication-assisted extraction (SAE) with liquid and gas chromatography for the analysis of solid agricultural and food samples. In addition, head-space techniques and direct thermal extraction are discussed. 

The Clianicteri/ation of Volatile and Semivolatile Components in Powdered turmeric by Direct Thermal Extraction Cas Cliromaloj>raphy—Mass Spectronictry... 

El-mass spectra were obtained for each component. Figures 7, B, 9 show the El-mass spectra for the three major components detected by direct thermal extraction GC-MS. Table III contains a list of the eight most abundant ions for the minor components in turmeric powder and their relative intensities. Figure 10 lists the structures fur the components detected. Some of these identifications are based on correlation with mass spectra in the NIST/EPA/NII ( Mass Spectra I library, I lowcver, the mass spectra for most of the components could not be found in the library and many of the structures in Figure 10 are proposed structures. For proposed structures, the identifications are ha.scd on similarities with components for which there was a good library match and by evaluation of the fragmentation patterns. 

Extraction of natural products yields complex mixtures of volatile, semi-volalile, and nonvolatile components. No one technique for obtaining mass spectral data for these components is generally applicable. Direct thermal extraction GC-M.S proved to be a valuable technique for the identification of volatile and semi-volatile components in powdered turmeric. 

Saffron, production, 66 Saffron flavor characterization using aroma extract dilution analysis aroma-active components, 74-78 detection of aroma-active component using OC-olfactometry, 67 experimental procedure, 67-68 volatile components, 68-74 Safranal, role in flavor, 66-78 Scmivolatile components in powdered turmeric, characterization using direct thermal extraction GC-MS, 80-96 Shallot, contribution of nonvolatile sulfur-containing flavor precursors to flavor, 53-63... 

Direct thermal extraction is a useful troubleshooting tool in polymer analysis. Kenion et al [1023]... 

R. D. Hiserodt, C.-T. Ho, and R. T. Rosen, The characterization of volatile and semivolatUe components in powdered turmeric by direct thermal extraction gas chromatography—mass spectrometry, in Spices Flavor Chemistry and Antioxidant Properties (S. J. Risch and C.-T. Ho, eds.), ACS Symposium Series 660, American Chemical Society, Washington, DC, 1997, p. 80. 

In a study on the identification of organic additives in rubber vulcanisates using mass spectrometry, Lattimer et al. [22] used direct thermal desorption with three different ionisation methods El, Cl and FI. Also, rubber extracts were examinated directly by four ionisation methods (El, Cl, FD and FAB). The authors did not report a clear advantage for direct analysis as compared to analysis after extraction. Direct analysis was a little faster, but the extraction methods were considered to be more versatile. 

SFE-GC-MS is particularly useful for (semi)volatile analysis of thermo-labile compounds, which degrade at the higher temperatures used for HS-GC-MS. Vreuls et al. [303] have reported in-vial liquid-liquid extraction with subsequent large-volume on-column injection into GC-MS for the determination of organics in water samples. Automated in-vial LLE-GC-MS requires no sample preparation steps such as filtration or solvent evaporation. On-line SPE-GC-MS has been reported [304], Smart et al. [305] used thermal extraction-gas chromatography-ion trap mass spectrometry (TE-GC-MS) for direct analysis of TLC spots. Scraped-off material was gradually heated, and the analytes were thermally extracted. This thermal desorption method is milder than laser desorption, and allows analysis without extensive decomposition. 

The amount of hydrocarbons present in the fire effluents have been measured in two different ways 1) amount of non-burnt hydrocarbons 2) soot was separated from gas with a glassfilter and latei extracted with cyclohexane. After the porous filter an absorbent glass-tube was connected with either charcoal or Tenax GC as the absorbent. Charcoal tubes were later extracted with carbon disulfide for analysis and Tenax tubes directly thermally desorbed t( a gas chromatograph and a mass spectrometer. 

For the extraction of sulfates and total sulfur a suitable acid and reducing agent, such as tin(II)-phosphoric acid (the Kiba solution of Sasaki et al. 1979) is needed. The direct thermal reduction of sulfate to SO2 has been described by Holt and Engelkemeier (1970) and Coleman and Moore (1978). Ueda and Sakai (1984) described a method in which sulfate and sulfide disseminated in rocks are converted to SO2 and H2S simultaneously, but analyzed separately. With the introduction of on-line combustion methods (Giesemann et al. 1994), multistep off-line preparations can be reduced to one single preparation step, namely the combustion in an elemental analyzer. Sample preparations have become less dependent on possibly fractionating wet-chemical extraction steps and less time-consuming. 

The high temperatures used for direct thermal desorption/extraction. Note that emissions testing is conventionally carried out at room temperature (Table 6.2) whereas VDA Method 278 for example requires desorption temperatures of 90 and 120 °C for volatiles and fogging compounds respectively. 

Bauer (1999b) found that the alkamide, dodeca-2 ,4E,8Z, 1 OE/Z-tetra-enoic acid isobutylamide, level was influenced by the preparation method. Nonthermal preparations appeared to have slightly higher levels of the tested alkamide than thermally treated products. Thus, the drying process may not be the best method for preparing Echinacea products. Pressing of the plant material to obtain an expressed juice is a common preparation method however, preservation of the juice with ethanol is required. Direct ethanol extraction of the plant material can be used in place of the pressing operation. 

Aroma compounds from vanilla beans have been extracted using several extraction procedures, using alcohols and organic solvents (Galletto and Hoffman, 1978 Dignum et al., 2002), direct thermal desorption (Hartman et al., 1992 Adedeji et al., 1993) and solid-phase microextraction (SPME) (Sostaric etal., 2000), followed by identification of the compounds by gas chromatography-mass spectrometry (GC-MS). 

Perez-CoeUo, M. S., Sanz, J., Cabezudo, M. D. (1997). Analysis of volatile components of oak wood by solvent extraction and direct thermal desorption-gas chromatography-mass spectrometry. J. Chromatogr. A, 778, 427 34. 

Thermal extraction techniques are usually performed in conjunction with gas chromatography. Petroleum hydrocarbons can be thermally desorbed from soil matrices at elevated temperatures. The eluting compounds are trapped in an absorbent phase such as Tenax and subsequently desorbed directly onto the column of the gas chromatograph. Whilst this technique is regarded as the closest to producing a real TPH value (C4-C35) it suffers from low sample size requirements (typically 1-10 mg) and is unlikely to be representative of the whole sample. Nevertheless, it can be used as a quick qualitative screening analysis. 

Headspace and thermal desorption are thermal extraction methods which can be directly connected to gas chromatography and do not need additional sample preparation. Usually both methods are applied for the determination of volatile compounds in air and water. Only few applications are known for the direct treatment of soil samples. The investigations for analysis of phenylarsenic compounds were carried out with an Headspace Sampler HS40 (Perkin-Elmer Inc.) and a Thermal desorption system TDS 2 (Gerstel GmbH, Germany). 

Where thermal desorption is inadequate to remove an analyte from the surface, a laser beam can be directed, focused or unfocused, against a solid, and compounds on surfaces of solids can be vaporized and ionized at ambient pressure in air. In one application of laser-based IMS to environmental analyses, soils contaminated with petroleum products were assayed for PAHs. In this, a laser was used to irradiate soil, vaporizing PAHs into the gas phase. This provided a direct, fast, extraction-free method for soil analyses. 

At temperatures below those normally required for the thermal decomposition of coal, the yields of extract vary directly with extraction temperature. This effect is usually most pronounced with the nonspecific solvents but it has been noted that a solvent such as ethylenediamine will produce from bituminous coal almost three times as much extract at its boiling point (115°C [240°F]) as at room tanperature and also enhances the effect of extraction with other solvents such as A-methyl-2-pynoUdone (Pande and Sharma, 2002). In fact, the yields of extracts obtained with a series of primary aliphatic amines have been found to vary with the extraction temperature rather than with any other solvent property. 

Ozel, M.Z. Gogus, F. Lewis, AC. (2006). Comparison of direct thermal desorption with water distillation and superheated water extraction for the analysis of volatile components of Rosa damascena Mill, using GCxGC-TOF/MS. Analytica Chimica Acta, Vol.566, pp. m- T7, ISSN 0003-2670... 

Chen, X. and Smart, R.B. 1992. Direct analysis of thin-layer chromatography spots by thermal extraction-gas chromatography-miass spectroscopy, J. Ghromatogr. Sci., 30 192-196. 

Steam-solvent distillation using diethyl ether has been used to remove and analyse for odour and taint from additives in food packaging films. Another technique that has been used is vacuum/thermal extraction. This procedure has been applied to polyamides and fluorocarbon polymers. The procedure is used for the direct isolation or release of volatile components from a polymeric matrix and may involve the combined use of vacuum and heat, as for example in the mass spectrometer direct insertion probe or during dry vacuum distillation. Alternatively, the volatiles may be swept from the heated sample by a flow of inert gas for concentration by freeze trapping and/or collection on to a solid adsorbent prior to thermal or solvent desorption for GC or mass spectrometric (MS) examination. 

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