Soxhlet extractions pressurized fluid extraction

S.B. Hawthorne, C.B. Grabanski, E. Martin and D.J. Miller, Comparison of Soxhlet extraction, pressurized liquid extraction, supercritical fluid extraction and subcritical water extraction for environmental solids recovery, selectivity and effects on sample matrix. J. Chromatogr.A 892 (2000) 421 133. 

Comparison of simple methanol extraction, Soxhlet extraction, pressurized liquid extraction (PLE), and supercritical fluid extraction (SFE) shows (Clausen et al., 2003) that DEHP can be extracted relatively easily from dust and that the effectiveness does not differ significantly between the different extraction methods (see Figure 2.4). Selection of the optimal method depends on several circumstances, for example number of extraction cycles, instrument accessibility and the analysis method. However, PLE using cyclohexane/acetone was chosen as the preferred extraction method in the field study. 

Amigo, S.G. Falcon, M.S.G. Yusty, M.A.L. Lozano, J.S. Supercritical Uqud extraction of polycycHc aromatic hydrocarbons from U ver samples and determination by HPLC-FL. Fresenius J. Anal. Chem. 2000, 367 (6), 572 578. Hawthorne, S.B. Grabanski, C.B. Martin, E. Miller, D.J. Comparison of Soxhlet extraction, pressurized liquid extraction, supercritical fluid extraction and subdritical water extraction for environmental solids Recovery, selectivity and effects on sample matrix. J. Chromatogr. A, 2000, 892, 421 33. 

Soxhlet extraction, pressurized fluid extraetion, sonication with ultrasound and supercritical fluid extraction... 

Ryno, M., L. Rantanen, E. Papaioannou, A.G. Konstandopoulos, T. Koskentalo, and K. Savela. 2006. Comparison of pressurized fluid extraction, Soxhlet extraction and sonication for the determination of polycyclic aromatic hydrocarbons in urban air and diesel exhaust particulate matter. J. Environ. Monit. 8 488 193. 

Yandenburg et al. [92] compared extraction of additive Irganox 1010 from freeze-ground polypropylene polymer by pressurized fluid extraction (PFE) and MAE with reflux, ultrasonic, shake-flask, and Soxhlet extraction. PFE and MAE were faster than any conventional method with comparable extraction efficiency. The times to reach 90% recovery by PFE using propan-2-ol at 150°C and acetone at 140°C were 5 and 6 minutes, respectively. Reflux with chloroform was found to be the fastest method performed under atmospheric pressure with 90% recovery in 24 minutes. Reflux with cyclohexane propan-2-ol (1 1) required 38 minutes. Ultrasonic, shake-flask, and Soxhlet extraction required about 80 minutes (90%) extraction). The total sample preparation time for PFE was 15 minutes, MAE 28 minutes, and reflux with chloroform was 45 minutes. 

Figure 7.17 Results obtained for the pressurized fluid extraction of DDT, DDD and DDE from contaminated soil, and comparison with those obtained from Soxhlet extraction , Soxhlet PFE 1, DDT 2, DDD 3, DDE [6] (cf. DQ 7.13).

Saim, N., Dean, J. R., Abdullah, M. P., and Zakaria, Z., Extraction of polycyclic aromatic hydrocarbons from contaminated soil using Soxhlet extraction, pressurized and atmosphereic microwave-assisted extraction, supercritical fluid extraction and accelerated solvent extraction,... 

Prior to extraction in a Soxhlet apparatus or by other related techniques such as pressurized fluid extraction (PFE), an anhydrous mixture is prepared usually by mixing wet sediment (excess water removed by decanting or low speed centrifugation) with anhydrous, precleaned sodium sulfate. Pre-drying of sediment (by freeze drying, oven or air drying) has been commonly employed but is not recommended for sediments with low levels of POPs because of possible contamination from laboratory air (Wallace et al., 1996 Alcock etal., 1994). 

Method 3545 uses pressurized fluid extraction at 100°C and a pressure up to 2000 psi to remove organophilic analyte species from dried solid samples including soils, clays, sediments, sludges, and waste soHds. Used for the extraction of semivolatile organic compoimds, organophosphorus pesticides, organochlorine pesticides, chlorinated herbicides, and PCBs, it requires less solvent and takes less time than the Soxhlet extraction described above. 

Nevertheless, to reach the adequate sensitivity limits in gas chromatography or liquid chromatography, independently on the detection technique used (mass-spectrometry or fluorescence, respectively), it results necessary to carry out preconcentration procedures as well as clean-up steps [52], The utilization of clean-up and preconcentration procedures introduces more sources of error in the analytical method, as well as increases the analysis time. The most common extraction-preconcentration procedmes are Soxhlet extraction, liquid-liquid extraction (LLE), ultrasoimd-assisted extraction (UAE), microwave-assisted extraction (MAE), pressurized fluid extraction (PFE), dialysis, solid-phase extraction (SPE), and solid-phase microextraction (SPME). 

Saponification—Liquid-hquid extraction Soxhlet extraction Ultrasound-assisted extraction Microwave-assisted extraction Pressurized liquid extraction Supercritical fluid extraction Matrix solid-phase dispersion... 

This cycle of vaporisation of the solvent, condensation, extraction, and vacuum-filtration may be repeated any number of times in a solid-fluid serial extractor. The occurrence of an extractive material fluid bed as a result of the flow of boiling hot vapour provides for effective extraction, while pressure filtration provides for short cycle times. This functional principle makes it possible to achieve filtration pressures which are 50-100 times more effective than when using the Soxhlet method, where only the low hydrostatic pressure of the extractive fluid operates. Solid-fluid-vortex extraction according to the proprietary FEXTRA (Feststoff Extraktion) principle is low cost. 

David and Seilier [1] compared the efficiencies of various extraction techniques including supercritical fluid [2], high pressure solvent and Soxhlet extraction for the removal of organophosphorus hydraulic fluids from soil. High pressure solvent extraction was at temperatures up to 200°C and pressures up to 170 bar was the favoured technique. Extraction efficiencies were similar in all three methods, but the favoured method was more rapid and cheaper to operate. 

As its name suggests, supercritical fluid extraction (SEE) relies on the solubilizing properties of supercritical fluids. The lower viscosities and higher diffusion rates of supercritical fluids, when compared with those of liquids, make them ideal for the extraction of diffusion-controlled matrices, such as plant tissues. Advantages of the method are lower solvent consumption, controllable selectivity, and less thermal or chemical degradation than methods such as Soxhlet extraction. Numerous applications in the extraction of natural products have been reported, with supercritical carbon dioxide being the most widely used extraction solvent. However, to allow for the extraction of polar compounds such as flavonoids, polar solvents (like methanol) have to be added as modifiers. There is consequently a substantial reduction in selectivity. This explains why there are relatively few applications to polyphenols in the literature. Even with pressures of up to 689 bar and 20% modifier (usually methanol) in the extraction fluid, yields of polyphenolic compounds remain low, as shown for marigold Calendula officinalis, Asteraceae) and chamomile Matricaria recutita, Asteraceae). " ... 

Hubert et al. [101] state that accelerated solvent extraction compared to alternatives such as Soxhlet extraction, steam distillation, microwave extraction, ultrasonic extraction and, in some cases, supercritical fluid extraction is an exceptionally effective extraction technique. Hubert et al. [ 101 ] studied the effect of operating variables such as choice of solvent and temperature on the solvent extraction of a range of accelerated persistent organic pollutants in soil, including chlorobenzenes, HCH isomers, DDX, polychlorobiphenyl cogeners and polycyclic aromatic hydrocarbons. Temperatures ofbetween 20 and 180 °C were studied. The optimum extraction conditions use two extraction steps at 80 and 140 °C with static cycles (extraction time 35 minutes) using toluene as a solvent and at a pressure of 15 MPa. 

Tocopherols consist of a, (3, y, and 8 isomers and are effective antioxidants. Oomah et al. (1997a) observed that y-tocopherol (9.04 mg/100 g seed) was the predominant isomer of Canadian flaxseed cultivars. Total tocopherol ( r = 0.42) and y-tocopherol (r = 0.41) values were correlated with seed oil content. Kamm et al. (2001) reported the distribution of tocopherols and tocotrienols in high and low linolenic flaxseed. Results were similar to the findings of Oomah et al. (1997a) in which y-tocopherol content was greater (430-575 mg/kg oil) in high ALA flaxseeds, whereas low linolenic flaxseed exhibited lower (170 mg/kg oil) values. Bozan and Temelli (2002) compared tocopherol levels in oil extracted by supercritical C02 fluid and soxhlet (Table XI). Soxhlet-extracted oil had greater tocopherol levels (76.4 mg/100 g oil). These authors speculated that the temperature-pressure combination may have influenced the tocopherol extraction by supercritical C02 fluid. 

In order to improve oxidative stability, supercritical C02 fluid extraction could be used for flaxseed oil extraction (Bozan and Temelli, 2002). This method demonstrated higher ALA content compared to soxhlet extraction. In contrast, tocopherol content was lower (Table XI). Temperature and pressure profiles did not alter the fatty add profile and exhibited similar results at 50 and 70°C and pressures of 35 and 55Mpa. Stability of oil was not reported, and since limited knowledge is available further research is required with regards to shelf life and comparisons to cold-pressing operation. 

A method for determining CDDs in municipal incinerator fly ash has been reported (Alexandrou and Pawliszyn 1990). The method uses supercritical fluid extraction (SFE) to recover CDDs from fly ash samples prior to GC. Supercritical fluid extraction is faster and less expensive than the typically used Soxhlet extraction and gives quantitative removal of CDDs and CDFs from fly ash. Extracts obtained using SFE will still require additional clean-up steps prior to analysis. Supercritical C02 has also been used to assist solvent-based extraction of CDDs from soils (Friedrich and Kleibohmer 1997). In this case, the supercritical fluid was combined with accelerated solvent extraction (liquid extractions conducted under elevated temperature and pressure) to provide good recoveries relative to Soxhlet extractions. 

Pressurized solvent extraction (PSE), also called pressurized fluid extraction (PEE), accelerated solvent extraction (ASE ), pressurized liquid extraction (PEE), or enhanced solvent extraction (ESE), is a solid-liquid extraction that has been developed as an alternative to conventional extractions such as Soxhlet, maceration, percolation, or reflux. It uses organic solvents at high pressure and temperature to increase the efficiency of the extraction process. Increased temperature decreases the viscosity of the liquid solvent, enhances its diffusivity, and accelerates the extraction kinetics. High pressure keeps the solvent in its liquid state and thus facilitates its penetration into the matrix, resulting in increase extraction speed [30]. 

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). 

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