Fast Soxhlet

Fast Soxhlet extractions 71 3.4.5 Microwave-assisted extractions. 104... 

As an alternative to traditional solvent extraction methods, the extraction by supercritical (SC) fluids has been used in tocol analysis. This is an environmentally friendly technique as little or no solvents are used. Extraction parameters, e.g. temperature and fluid density, are easily optimized and managed, and as the extraction is fast it is thus suitable for routine work with many samples. SC carbon dioxide has been used to extract tocols from barley (Fratianni et al, 2002), dried bay leaves (Gomez-Coronado et al, 2004), and garden cress seeds (Diwakar et al, 2010). Extractions were carried out in single or multiple steps and with different fluid densities controlled by extraction pressures. Tocol yields from barley were 5% and 14% less than by Soxhlet and chloroform-methanol extractions (Fratianni et al, 2002), yields from garden cress seeds were 26% less than by Soxhlet extraction (Diwakar et al, 2010), and a- and y-tocopherol yields from dried bay leaves were 22% and 40% less than by acetone extraction (Gomez-Coronado et al, 2004). Despite lower recoveries of tocols, the SC carbon dioxide extraction methods were considered comparable to the classical extraction methods (Fratianni et al, 2002). 

Ultrasound-assisted extraction (USE) is an effective method for leaching many analytes from different kinds of samples [52-55]. It is simple, fast, efficient, and inexpensive in comparison with conventional extraction techniques such as solvent extraction in the Soxhlet apparatus. Ultrasound-assisted solid-liquid extraction is an effective and time-saving extraction method. Sonication accelerates the mass-transfer process between two phases. Use of ultrasound results in a reduction in operating temperature, allowing the extraction of temperature-sensitive components. The ultrasound apparatus is cheaper and its operation is easier in comparison with other novel extraction techniques such as MAE. 

Soil, sediment, and dust samples were prepared in a similar way before analysis. After the pre-cleanup steps and homogenization, FRs were extracted from samples using different solid-liquid extraction techniques. The most commonly used technique was accelerated solvent extraction (ASE), which enables the fast extraction of samples using different solvents such as hexane and dichloromethane [98-100]. Other commonly used techniques for these samples were ultrawave-assisted extraction (UAE) [97], which also enabled quick extraction, and the more time-consuming but very efficient technique, Soxhlet extraction [96]. Some authors have also described less common techniques such as microSPE [95]. There is also information that many FRs that are no longer produced (mainly PCBs and PBDEs) are present in dusts, soils, and sediments in very high amounts, even 390 pg/g [98]. 

A fast stream of is Introduced into IN hydrochloric acid at —2 to —4°C simultaneously, a cooled solution of HAUCI4 4 H3O is allowed to flow in. The black precipitate is digested with water, washed free of acid, treated with alcohol and ether, extracted with CSa in a Soxhlet extractor, washed with ether, and dried in vacuum over PSO5. 

There is a fast extraction system available (Tecator Soxtec) (Figure 17.18), which uses hot solvent, heated indirectly by hot circulating oil. It is about five times faster than a conventional cold soxhlet extraction and up to 65% of the solvent can be recovered at the end of the extraction... 

The traditional method of determining the spin-finish on fibres, be it polyester (PET) staple fibres or UHMWPE (Dyneema) fibres, is by Soxhlet extraction. Products with concentrations of 0.1% can be easily investigated by LR-NMR [218]. LR-NMR in spin-echo sequence has been used as an alternative to extraction methods for fast spin-finish determinations where the concentration of oil on the yarn is the only desired information [219]. In this procedure the signal of polymer protons and adsorbed water molecules decays during 70-100 /zs after excitation, while the remaining signal is due to the oily spin-finish. Depending on proper calibration and method adjustment an accuracy of 0.02% absolute at a spin-finish level of 0.3-0.8% can be reached. 

The classical approach to extract PAHs from lipophilic compounds which are abundant in marine matrices is by means of saponification in basic (NaOH or KOH) alcoholic solution [indicatively see (Webster et al. 2006 Rank 2(X)9)] or the Soxhlet extraction with organic solvents mainly acetone, n-hexane and DCM [indicatively see (Vorkamp et al. 2010 Yoshimine et al. 2012)]. Both methods are widespread, but time consuming. For this reason more fast methods which reduce time, labour and solvent use were pursued by researchers. These include Sonication Assisted Extraction (Maioli et al. 2010 Dsikowitzky et al. 2011), Microwave Assisted Liquid Extraction (MAE) (Cortazar et al. 2008 Zuloaga et al. 2009), and Accelerated Solvent Extraction or Pressurized Liquid Extraction (ASE) usually conducted with the Dionex system (Sloan et al. 2004). Finally the matrix solid-phase dispersion (MSPD) has also been applied to extract PAHs from mussels even in miniaturized scale (Campins-Falco et al. 2008). 

Conventional techniques, that is, Soxhlet extraction, for the extraction of active constituents are time and solvent consuming, thermally unsafe and the analysis of numerous constituents in plant material is limited by extraction step. High and fast extraction ability with less solvent consumption and protection offered to thermo-labile constituents are the attractive features of this new and promising microwave-assisted extraction (MAE) technique (Mandal et al., 2007). 

The pressure in PLE is not a significant variable to optimize, because its role is simply to maintain the solvent in its liquid state. The main variables to optimize are extraction time and temperature, which considerably simplifies the experimental design. The main advantages of PLE are fastness (around 15 min), low amounts of toxic organic solvents are required (between 15 and 40 mL), and several samples can be extracted simultaneously (up to 24). However, the instrumentation is much more expensive than Soxhlet or even microwaves. EPA method 3545 uses PLE in the determination of semivolatile organic compounds from solid samples [139], which can be extended to solid devices used to trap PAHs in air monitoring. Furthermore, PLE has proven to be an efficient method to extract analytes from complex samples, with efficiencies comparable to Soxhlet extraction [140],... 

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