Pressurized liquid extraction

Extraction method USEPA method Avg. volume of solvent (mL) Avg. extraction time A uisition cost Operating cost/sample 

Soxhlet extraction 3540C 300 16-24h Very low Very high 

Supercritical fluid extraction 3560/3561/ 3562 10 20-50 min Moderate to high Moderate to high 

Thermal degradation does not occur during PFE extractions. Using PFE techniques, the sample is completely and constantly surrounded by solvent thus, oxidative losses are minimized if the extraction solvent is degassed and oxygen is excluded. Since the analytes are in the heated zone for only short periods of time, thermal losses do not occur if appropriate temperatures are used for the extractions. 

Traditional techniques, such as Soxhlet, can take 4-48 h. With PFE, analyte recoveries equivalent to those obtained using traditional extraction methods can be achieved in only 15-30 min. Although PFE uses the same aqueous and organic solvents as traditional extraction methods, it uses them more efficiently. A typical PFE extraction is done using 50-150 mL of solvent, see Table 2.6 for comparison. 

A relatively new automated extraction method is PLE, also called accelerated solvent extraction (ASE), which is based on an extraction under elevated temperature (50-200°C) and pressure (3-205 bar) during a short period of time (5-15 min). This technique has been used for the extraction of phenolic compounds from foods such as vegetables and fruits. In PLE, a solid sample is packed into the extraction cell and analytes are extracted from the matrix with conventional low-boiling solvents or solvent mixtures at elevated temperatures up to 200°C and pressure (30-200 bar) to maintain the solvent in the liquid state [61]. 

A very interesting feature of this technique is the possibility of full automation, and many samples can be extracted sequentially. However, the extraction efficiency of PLE is dramatically influenced by extraction pressure and temperature conditions, and a sample matrix can also affect the extraction efficiency [61]. Therefore, the optimization of the extraction conditions should be carefully evaluated in order to get suitable results. 

In this sense, some authors [49] evaluated different parameters, such as percentage of methanol, temperature, pressure, and static extraction time for the extraction of phenolic compounds from apple samples, obtaining the best results when the following conditions were used pure methanol as solvent, extraction temperature of 40°C, pressure 69 bars, and 5 min static extraction time. 

According to Luthria [63], PLE is effective for the extraction of phenolic acids from potato peels, and a variety of parameters were optimized. The results indicated that the optimum recoveries were obtained when phenolic acids were extracted using methanohwater (90 10, v/v) at 160°C. It has been shown that static time variations (5-15 min), pressure (35-138 bars), and flush volume (10-100%) variations did not significantly improve the extraction. Luthria [64] also optimized the extraction conditions of phenolic acids in parsley, with similar results as in potato peels, but in this case, all extractions were carried out with either one or two solvent mixtures, ethanoliwater (50 50, v/v) and/or acetone water (50 50, v/v), as it has been indicated in Table 16.4. 

This technique is used for the extraction of semi-volatile or nonvolatile analytes from liquid samples or from solid samples, which have been previously extracted. This is based on the adsorption of the analytes into a solid sorbent and then eluted with a suitable solvent. The type of solvent chosen for the elution of the target compounds depends on the kind of sorbent and the polarity of each analyte. SPE technique can be performed in the off- and online modes, although the online approach is preferred due to advantages such as higher sensitivity and less sample handling. 

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General trends are focused on reduced-solvent extractions or adsorption-based methods — enviromnentaUy friendly solvents for both solid and liquid samples. In recent decades, advanced techniques like supercritical fluid extraction (SFE), ° pressurized liquid extraction (PLE)," microwave-assisted extraction (MAE), ultrasound-assisted extraction, countercurrent continued extraction (www.niroinc.com), solid... 

Yong Ju, Z. and Howar, L.R., Effects of solvent and temperature on pressurized liquid extraction of anthocyans and total phenolics from dried red grape skin, J. Agric. Food Chem., 51, 5207, 2003. 

Henry, M.C. and Yonker, C.R., Supercritical fluid chromatography, pressurized liquid extraction, and supercritical fluid extraction. Anal. Chem., 78, 390, 2006. 

In the past decade, new sample extraction techniques have been introduced to meet stricter criteria in the areas of food and agriculture, for example, enviromnentally friendly, non-toxic, fast, automated, robust, and cost-efficient techniques. Accelerated solvent extraction (ASE) and pressurized liquid extraction (PEE) are two methods developed for the extraction of chemicals of interest " and provide high yields and efficiency from a wide range of botanical, - animal, and biological samples. ASE and PLE combine solvents at elevated temperatures (40 to 200°C)... 

Peres, V.P. et al.. Comparison of soxhlet, ultrasound-assisted and pressurized liquid extraction of terpenes, fatty acids and vitamin E from Piper gaudichaudianum Kunth, J. Chromatogr. A, 1105, 115, 2006. 

PLE pressurized liquid extraction, SPE solid phase extraction, UE ultrasonic extraction, DSPE dispersive solid phase extraction, SBSE stir bar sorptive extraction, TD-GC-MS thermal desorption-gas chromatography-mass spectrometry, LAS linear alkylbenzene sulfonates, CDEAs coconut diethanol amides, NPEOs nonylphenol ethoxylates, DP degradation products, SPC sulphenyl carboxylates, PCDD dibenzo-p-dioxins (PCDD), PCDF dibenzofurans, PCBs biphenyls... 

Schroder, H.E (2003). Determination of fluorinated surfactants and their metabolites in sewage sludge samples by liquid chromatography with mass spectrometry and tandem mass spectrometry after pressurized liquid extraction and separation on fluorine-modified reversed-phase sorbents. J. Chromatogr. A 1020(1), 131-151. 

The main drawback of this technique is solvent and time-consuming. In the last decade, there have been efforts to develop extraction techniques that allow efficient extraction and reduced solvent volumes in shorter times, incorporating high levels of automation, such as pressurized liquid extraction (PLE) [commonly known as accelerated solvent extraction (ASE)]. 

Andreu V, Ferrer E, Rubio JL, Font G, Pico Y (2007) Quantitative determination of octylphenol, nonylphenol, alkylphenol ethoxylates and alcohol ethoxylates by pressurized liquid extraction and liquid chromatography-mass spectrometry in soils treated with sewage sludges. Sci Total Environ 378 124—129... 

Jelic A, Petrovic M, Barcelo D (2009) Multi-residue method for trace level determination of pharmaceuticals in solid samples using pressurized liquid extraction followed by liquid chromatography/quadrupole-linear ion trap mass spectrometry. Talanta 80 363-371... 

A rapid and simple method for PBDE and HBCD determinations in sediment and fish samples was used. The analytical method was based in selective pressurized liquid extraction (SPLE) [21] without further cleanup step and analysis by gas chromatography coupled to mass spectrometry (GC-MS), working with negative ion chemical ionization (NCI) [22, 23],... 

Analysis of pesticides (eight in total, namely, molinate, propanil, fenitrothion, malathion, bentazone, cypermetrine, maloxon, and fenitrothion oxon) in biota was accomplished with a method based on pressurized liquid extraction (ASE), followed by SPE clean-up, and analysis by gas chromatography-mass spectrometry with electron impact ionization (GC/MS-EI). 

Petrovic M, Lacorte S, Viana P, Barcelo D (2002) Pressurized liquid extraction followed by liquid chromatography-mass spectrometry for the determination of alkylphenolic compounds in river sediment. J Chromatogr A 959 15-23... 

Schltisener MP, Spiteller M. Bester K. Determination of antibiotics from soil by pressurized liquid extraction and liquid chromatography-tandem mass spectrometry. J. Chromatogr. A 2003 1003 21-28. 

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. 

Wan, J. B., Yang, F. Q., Li, S. P., Wang, Y. T., and Cui, X. M. (2006b). Chemical characteristics for different parts of Panax notoginseng using pressurized liquid extraction and HPLC-ELSD. /. Pharm. Biomed. Anal. 41, 1596-1601. 

In 2003, Smith reviewed newer sample preparation techniques, including pressurized liquid extraction, solid phase microextractions, membrane extraction, and headspace analysis. Most of these techniques aim to reduce the amount of sample and solvent required for efficient extraction. 

Mohn T, Cutting B, Ernst B, Hamburger M (2007) Extraction and analysis of intact glucosinolates-a validated pressurized liquid extraction/liquid chromatography-mass spectrometry protocol for Isatis tinctoria, and qualitative analysis of other cruciferous plants. J Chromatogr 1166 142-151... 

Barron L, Tobin J, Pauli B (2008) Multi-residue determination of pharmaceuticals in sludge and sludge enriched soils using pressurized liquid extraction, solid phase extraction and liquid chromatography with tandem mass spectrometry. J Environ Monit 10 353-361... 

Postigo C, Alda MJLd, Viana M, Querol X, Alastuey A, Artinano B, Barcelo D (2009) Determination of drugs of abuse in airborne particles by pressurized liquid extraction and liquid chroma-tography-electrospray-tandemmass spectrometry. Anal Chem 81(ll) 4382-4388... 

In mercury speciation studies, pressurized liquid extraction (PLE), microwave-assisted extraction (MAE), and supercritical fluid extraction (SEE) are employed [33]. In particular, methyl-mercury is extracted by the Westoo method [33,34], which consists in a leaching process with hydrochloric acid, the extraction of the metal chloride into benzene or toluene, the addition of ammonium hydroxide that converts the metal species to hydroxide and the saturation with sodium sulfate. Most of the HPLC methods reported in literature for the determination of organomercury compounds (mainly monomethyhnercury, monoethyhnercury, and monophenylmercury) are based on reversed... 

Some authors [467,468] use novel extraction techniques, such as pressurized liquid extraction (PLE) and SEE obtaining recovery higher than with saponification. 

J. Gomez-Ariza, M.-A. Caro-de-la-Torre, I. Giraldez and E. Morales, Speciation analysis of selenium compounds in yeasts using pressurized liquid extraction and liquid chromatography-microwave-assisted digestion-hydride generation-atomic fluorescence spectrometry. Anal. Chim. Acta, 524(1-2), 2004, 305-314. 

J. Moreda-Pineiro, E. Alonso-Rodriguez, P. Lopez-Mahia, S. Muniategui-Lorenzo, D. Prada-Rodriguez, A. Moreda-Pineiro and P. Bermejo-Barrera, Determination of major and trace elements in human scalp hair by pressurized-liquid extraction with acetic acid and inductively coupled plasma-optical-emission spectrometry. Anal. Bioanal. Chem., 388(2), 2007, 441 449. 

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