Subcritical solvent extraction

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. ... 

Monrad JK, Howard LR, King JW, Srinivas K, Mauromoustakos A (2010) Subcritical solvent extraction of anthocyanins from dried red grape pomace. J Agric Food Oiem 58(5) 2862-2868... 

Pressurized liquid extraction (PLE), also known as accelerated solvent extraction (ASE) or subcritical solvent extraction, uses solvents utilized in standard hquid extraction at high pressures and temperatures above their boiling points to shorten the extraction time, reduce solvent usage, and increase extraction efficiency. At elevated temperatures (50-200°C), diffusivity increases, mass transfer improves, solubility increases, and the interactions between solute and matrices is minimized. At high pressures (500-3,000 psi), the penetration of the solvent is also improved (Richter et al. 1996). Subcritical water extraction (SWE), used to recover catechins and proanthocyanidins from wine pomace and sequential extraction at different temperatures (50 C, 100 C, and 150°C) was reported to have the highest recovery, but different flava-... 

Organic solvent-less techniques (e.g. subcritical water extraction, headspace SPME). 

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... 

Extraction of stevia sweeteners from dried leaves can be accomplished with acetonitrile in the presence of calcium carbonate solution (116) or with boiling water adjusted to pH 9.0 (107). Ahmed and Dobberstein (117) extracted stevioside and rebaudioside A and C from dried leaves of S. rebaudiana in a micro-Soxhlet apparatus. They observed that chloroform/methanol provided the best results, compared to chloroform or to chloroform/methanol/water. Extraction of stevioside, rebaudioside A and C, and dulcoside A can also be performed by subcritical fluid extraction using C02 and methanol as a modifier. Such an extraction technique has been gaining popularity as an analytical tool because it is rapid, simple, and less expensive in terms of solvent cost (110). Beverages, tabletop sweeteners, beverages containing pulp, and candies are prepared as indicated in Sec. I.C (110,115,118). 

Supercritical fluid extraction [153,154], accelerated solvent extraction [68] and subcritical fluid extraction [107,155] have been studied. To reduce the equipment cost and the analysis time in the extraction process and sample preconcentration, a solid-phase microextraction method was proposed by Pawliszyn and coworkers [156-158]. 

Wennrich et al. [167] investigated the capabilities of coupling accelerated solvent extraction with water as the extraction solvent and solid-phase microextraction to determine chlorophenols in polluted soils. Subcritical water extraction was performed using a commercially available accelerated solvent extractor. This system solves the problem of the analytes partitioning back to the soil matrix, which can occur in straightforward subcritical water extraction because in the Wennrich et al. method [167] the aqueous phase and the soil are separated under the extraction conditions. 

Solvent extraction Microwave extraction Solid phase microextraction Subcritical water extraction Subcritical water extraction Supercritical fluid extraction... 

Fig. 2 Gas chromatography-flame ionization detection chromatograms containing early artifact peaks from different solvent extraction methods Soxhlet, ASE (pie), SEE, and subcritical water extraction of a soil sample collected from a manufacturing gas plant site. The numbers refer to PAHs identified in the legend of Fig. 1. (From Ref. [12].)...

Williams JR, Morgan ED, Law B. Comparison of supercritical, subcritical, hot, pressurised and cold solvent extraction of four drugs from rodent food. Anal Commun 1996 33 15-17. 

The most important extraction technique nowadays is simple solvent extraction. The traditional solvent for extraction was benzene, but this has now been superseded by other solvents because of concern over possible toxic effects of benzene on those working with it. Petroleum ether, acetone, hexane and ethyl acetate, together with various combinations of these, are typical solvents for extraction. Recently, there has been a great deal of interest in the use of carbon dioxide as an extraction solvent. Both supercritical carbon dioxide and subcritical liquid carbon dioxide are used, depending on circumstances. The pressure required to liquify carbon dioxide at ambient temperature is considerable and thus the necessary equipment is expensive. This is reflected in the cost of the oils produced but carbon dioxide has the advantage that it is easily removed and there are no concerns about residual solvent levels. The major applications of liquid carbon dioxide extraction are in decaffeination of coffee and extraction of hops. 

The rosemary subcritical water extractions were carried out at 60 and 100 °C for 25 min. The procedure was as follows 2.0 g of sample were placed in 11 mL extraction cells prior to each extraction a heat-up time of S min was completed. The extracts obtained were inunediately protected from light and stored under refrigeration until dried. For this purpose, a Freeze Dryer (Unitop 400 SL, Virtis, Gardiner, NY, USA) was used. After freeze-drying, 10 mg of each extract were freshly dissolved in 1 ml of water and immediately injected into CE-MS without further purification. Water was deoxygenated by purging with He for 15 min prior its use as extraction solvent. 

Selective extraction solvent (SWE - subcritical water extraction) Fractionating agent (SWF - subcritical water fractionation) Reaction medium (SWR - subcritical water reaction)... 

In pressurized liquid extraction (PLE), rapid extraction is performed with small volumes of conventional solvents by using high temperatures (up to 200°C) and high pressures (up to 20 000 kPa) to maintain the solvent in a liquid state. The extraction can also be done with a purely aqueous phase, a technique often referred to as pressurized hot water extraction (PHWE) or subcritical water extraction. Temperatures of up to 325 C have been used in PHWE 29-38). 

Many of the above-mentioned advantages also apply to liquids that have been raised to near-supercritical (but subcritical) regions (20). These properties are exploited in accelerated solvent extraction that employs high pressure at elevated temperatures. The increased temperature also increases the volatility of the analytes and their solubility in the solvent. Thus SFE may be... 

Eight micro liter of octane extraction solvent was placed inside a porous, polypropylene fiber following an 8 min analyte preconcentration step, 4 fil of extract was injected into a gas chromatograph Static subcritical water extraction was coupled with styrene-DVB (SDB-XC) extraction discs soil, water, and the SDB-XC disc are placed in a sealed extraction cell, heated to 250°C for 15 to 60 min, cooled, and the PAHs recovered from the disc with acetone/methylene chloride With a Soxhlet apparatus (18 h), by PLE (50 min at 100°C), SEE (1 h at 150°C with pure CO2), and subcritical water (1 h at 250°C, or 30 min at 300°C)... 

When water is used as the solvent, PLE is referred to as superheated water extraction, subcritical water extraction (SWE), or pressurized (hot) water extraction (PWE). Hot water is very effective as an extraction solvent for PAHs from soil and sediment. Superheated water is water above the boiling point but below the supercritical point, and under sufficient pressure to maintain... 

Extraction of herbicides from solid matrixes has frequently been done by Soxhlet extraction, which required large volumes of solvent and was a time consuming process. Therefore, new extraction techniques have been developed and applied for the past ten years. Herbicides and their main metabolites can be extracted from sohd samples by these new methods such as, SFE, subcritical water extraction (SWE), microwave-assisted extraction (MAE), or pressurized fluid extraction (PFE). From a general point of view. Camel evaluated potentials and pitfalls of SEE, MAE, and PFE. ... 

Hawthorne SB, Trembley S, Moniot CL, Grabanski CB, Miller DJ (2000) Static subcritical water extraction with simultaneous solid-phase extraction for determining polycyclic aromatic hydrocarbons on environmentals solids. J Chromatogr A 886 237-244 Hubert A, Wenzel KD, Manz M, Weissflog L, Engewald W, Scheuermann G (2000) High extraction efficiency for POPs in real contaminated soil samples using accelerated solvent extraction. Anal Chem 72 1294—1300... 

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. 

SEE is today not the only hyphenated extraction technique available. Both microwave-assisted solvent extraction (MAE) and pressurized fluid extraction (PEE) have evolved in parallel with SFE during the last decade. A thorough comparison of the different techniques can be found in the analytical literature, and will assist in choosing an appropriate technique for a specific application. These newer techniques offer both speed and simplicity, while some of the main benefits of SFE are still inherent to the usage of supercritical fluids as MAE and PFE utilize liquid solvents. More recently, subcritical water extraction has also been introduced as an environmental friendly alternative but the reader is referred to the analytical literature on this research topic. 

Accelerated solvent extraction (ASE), focused microwave soxhiet extraction (FMSE), immuno affinity cleanup (im-Cu), liquid-liquid extraction (LLE), low-temperature lipid precipitation (LTLP), matrix solid-phase dispersion (MSPD), microwave-assisted extraction (MAE), nanofiltration (NF), pressurized fluid extraction (PEE), single drop microextraction (SOME), solid-phase extraction (SPE), solid-phase microextraction (SPME), steam distillation (SD), stir bar sorptive extraction (SBSE), surpercritical fluid extraction (SFE), subcritical fluid extraction (ScFE), supported liquid membrane extraction (SLME), ultra-sonication (US), size exclusion chromatography (SEC), liquid chromatography-fraction collection (LC)... 

A, acaricide AV, avicide I, insecticide F, fungicide H, herbicide GR, growth regulator N, nematocide R, rodenticide US, ultrasonication LLE, liquid-liquid extraction CU, cleanup ImCU, immuno cleanup SPE, solid-phase extraction MSPD, matrix solid-phase dispersion SBSE, stir bar sorptive extraction SD, steam distillation FMSE, focused microwave Soxhiet extraction PFE, pressurized fluid extraction ASE, assisted solvent extraction ScFE, subcritical fluid extraction SFE, supercritical fluid extraction SEC, size-exclusion chromatography LC, liquid chromatography (fraction collection) LTLP, low temperature lipid precipitation. 

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