Hot solvent extraction

The first step for the determination of PAHs is removal from the matrix by solvent extraction, which preferably is performed with boiling toluene or benzene (hot solvent extraction by refluxing see Jacob and Grimmer 1994), although other solvents (e.g. tol-uene/acetone, acetone, and dichloromethane) and other extraction procedures (ultrasonic treatment, Soxhlet extraction, and accelerated solvent extraction) can also be applied. 

In liquid-solid extraction (LSE) the analyte is extracted from the solid by a liquid, which is separated by filtration. Numerous extraction processes, representing various types and levels of energy, have been described steam distillation, simultaneous steam distillation-solvent extraction (SDE), passive hot solvent extraction, forced-flow leaching, (automated) Soxh-let extraction, shake-flask method, mechanically agitated reflux extraction, ultrasound-assisted extraction, y -ray-assisted extraction, microwave-assisted extraction (MAE), microwave-enhanced extraction (Soxwave ), microwave-assisted process (MAP ), gas-phase MAE, enhanced fluidity extraction, hot (subcritical) water extraction, supercritical fluid extraction (SFE), supercritical assisted liquid extraction, pressurised hot water extraction, enhanced solvent extraction (ESE ), solu-tion/precipitation, etc. The most successful systems are described in Sections 3.3.3-3.4.6. Other, less frequently... 

An important example illustrating the difficulties in this area is Ir4(CO)i2, which is only accessible on a preparative scale in sufficient and reproducible purity using particular techniques such as a continuous hot solvent extraction. 

Askari et al. [15] have compared purge and trap, methanol immersion and hot solvent extraction methods for the determination of volatile organic compound in aged soil. These workers found that hot solvent extraction is much more effective than the US Environmental Protection Agency approved purge and trap technique [7, 8]. 

The SA binder is tested for dispersion and particle size prior to mix production with a microscope. The binder level of the mix is constantly measured with a Troxler model 2226 asphalt content gauge. Hot solvent extraction (ASTM D2172) using tetrachloroethylene solvent can also be used to measure the binder content of a SA mix. The sulfur—asphalt ratio of the binder is monitored in the field with the Troxler or by density measurements. Other methods that can be used to measure SA ratios are x-ray fluorescence of solutions of sulfur-asphalt in tetrachloroethylene, liquid chromatography, and differential scanning calorimetry. X-ray fluorescence measures total sulfur, liquid chromatography determines elemental sulfur, and DSC monitors crystalline sulfur. 

The so-called solvent extraction method by toluene, o-xylene or carbon disulfide is the most common and frequently used extraction method, in which metallofullerenes and hollow fullerenes are preferentially dissolved in solvents. The so-called Soxhlet extraction (a continuous and hot solvent extraction) or ultrasonic extraction is normally employed to increase the solvent extraction efficiency (Khemani et al., 1992). Insolubles in soot are easily separated from this solution by filtration. However, in many cases, the toluene or CS2 extraction is not sufficient, since nearly half of the metallofullerene still remains in the residual soot even after the extensive CS2 extraction. It has been found that metallofullerenes are further extracted from the residual soot by such solvents as pyridine (Inakuma et al., 1995) and 1,2,4-trichlorobenzene (Yamamoto et al., 1994a,b). The metallofullerenes were found to be concentrated in this pyridine or trichlorobenzene extracted fraction. When necessary, the metallofullerene extracts can be stored in carbon disulfide solution for an extended period of time, up to a year. 

Camptothecin (43) was first isolated by Monroe Wall and Mansukh Wani in 1966, after ethanolic extracts of Camptotheca acuminata, a tree native to China, showed unusual and potent antitumor activity (63). Starting with 19 kg of dried wood and bark. Wall and Wani painstakingly purified the principal active component with a combination of hot solvent extraction, an 11-stage Craig countercurrent partition process, silica gel chromatography, and crystallization. Camptothecin was characterized as a novel pentacyclicalkaloid, present as j ust 0.01 % w/w of the stem bark of C ax umi-... 

Static pressurized hot solvent extraction (SPHSE), which shall henceforward be referred to as accelerated solvent extraction (ASE) for the reasons stated above, is the less flexible PHSE mode in terms of alteration or coupling to other techniques but is so far the more widely used — in fact, it accounts for over 65% of the PHSE publications reported since 1994. This is mainly the result of the sole commercially available extractor (the Dionex 200 model) implementing the static mode alone and also of the large number of studies conducted by different or even the same authors on the same analytes in the same matrices, which have therefore contributed little or nothing new in this area [58-63]. 

As can be seen from Fig. 6.9, dynamic pressurized hot solvent extraction (DPHSE) has evolved similarly to ASE however, as noted earlier, DPHSE has been the subject of many fewer reports, primarily as a result of the lack of commercially available equipment for implementation. In any case, the relatively scant reported applications of DPHSE are of especial interest as regards automation of the analytical process in fact, the dynamic nature of the system facilitates its coupling to other dynamic systems with a view to accomplishing preconcentration [39,42,45,145], filtration [42,45], chromatographic separation [145,146], derivatization [46,57] and detection [44,147], among others, and the partial or total automation of the analytical process. 

Fig. 6.10. Typical experimental set-up for dynamic pressurized hot solvent extraction (DPHSE). SR solvent reservoir, HPP high-pressure pump, IV inlet valve, OV outlet valve, PH pre-heater, EC extraction cell, C cooler, R restrictor.

The steps involved in a dynamic pressurized hot solvent extraction process are similar to those of ASE, with only a few, slight differences — particularly at the last stages. Thus, the DPHSE process involves the following five steps (see Fig. 6.13) ... 

Like ASE, pressurized hot solvent extraction has been virtually exclusively applied to solid samples. There is only a single reported use with liquid samples that involved altering the extractor and is dealt with separately at the end of this section on account of its innovative character. As in ASE, most applications are concerned with environmental samples there are however, several interesting uses in the biological field. This section discusses the more interesting applications of DPHSE in terms of the matrix types and analytes involved. 

Modification of fish proteins by proteolytic enzymes to increase their solubilities illustrates a variety of techniques and approaches. Basically, three general enzymic methods have been used to prepare fish proteins or hydrolysates with altered solubilities and other functionalities. These methods include (a) the enzymic solubilization of fish protein concentrate prepared by hot solvent extraction of fish, (b) the enzymic modification of myofibrillar proteins extracted from fish with 0.6M NaCl, and (c) the proteolysis of whole fish to prepare biological fish protein concentrate (FPC). 

Some components of organic phosphorus may also be extracted using organic solvents. Phospholipids, for example, which are used as biomarkers for microbial communities, can be extracted using methanol-chloroform-water (White et al., 1979), by pressurized hot solvent extraction (Macnaughton et al., 1997), cold methanol-water, or a surfactant such as Triton X-100 (Amini, 2001). 

Macnaughton, S.J., Jenkins, T.L., Wimpee, M.H., Cormier, M.R. and White, D.C. (1997) Rapid extraction of lipid biomarkers from pure culture and environmental samples using pressurized accelerated hot solvent extraction. Journal of Microbiological Methods 31,19-27. 

Pressurized liquid extraction (PEE) has received numerous names, such as accelerated solvent extraction (ASE), pressurized fluid extraction (PEE), pressurized hot-solvent extraction (PHSE), subcritical solvent extraction (SSE) and hot-water (H2O) extraction (HWE). PEE is carried out at temperatures above the boiling point of the solvent and uses high pressure to maintain the solvent in the liquid phase and achieve fast and efficient extraction of analytes from the solid matrix. HWE is being increasingly used in residue analysis, due to low cost, low toxicity, and ease of disposal. At ambient temperature and pressure H2O is a polar solvent, but if the temperature and pressure are increased, the polarity decreases considerably, and H2O can be used to extract medium to low polarity analytes. ... 

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