Pressure microwave-assisted extraction

Example 7.5 Pressurized Microwave-Assisted Extraction of Polycyclic Aromatic Hydrocarbons from Contaminated Soil... 

Figure 7.14 Results obtained for the pressurized microwave-assisted extraction of various polycyclic aromatic hydrocarbons from contaminated soil, and comparison with those obtained from Soxhlet extraction , Soxhlet HI, pMAE 1, naphthalene 2, acenaphthylene 3, acenaphthene 4, fluorene 5, phenanthene 6, anthracene 7, fluoranthene 8, pyrene 9, benz[a]anthracene 10, chrysene 11, benzol, ]fluoranthene 12, benzo[a]pyrene 13, indeno[l,2,3-cd]pyrene 14, benzo[g/ /]pyrene [1] (cf. DQ 7.11).

First of all, it is important to identify what the acronyms represent. The following have been used aMAE, atmospheric microwave-assisted extraction SFE, supercritical fluid extraction pMAE, pressurized microwave-assisted extraction PFE, pressurized fluid extraction ASE, accelerated solvent extraction MSPD, matrix solid-phase dispersion. 

L. 2008. Analysis of ginsenosides in Panaxginseng in high pressure microwave-assisted extraction. Food Chemistry 110 161-167. 

Liu Z, Yan G, Bu F, Sun J, Hu X, Zhang H (2005) Analysis of chemical composition of Acanthopanax senticosus leaves applying high-pressure microwave-assisted extraction. Chem Anality 50(5) 851-861... 

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... 

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... 

Kaufmann, B. and Christen, P., Recent extraction techniques for natural products microwave-assisted extraction and pressurized solvent extraction, Phytochem. Anal., 13, 105, 2002. 

In extraction, analyte is dissolved in a solvent that does not necessarily dissolve the entire sample and does not decompose the analyte. In a typical microwave-assisted extraction of pesticides from soil, a mixture of soil plus acetone and hexane is placed in a Teflon-lined bomb (Figures 28-8 and 28-13) and heated by microwaves to 150°C. This temperature is 50° to 100° higher than the boiling points of solvents at atmospheric pressure. Pesticides dissolve, but the soil remains behind. The liquid is then analyzed by chromatography. 

Camel, V. 2001. Recent extraction techniques for solid matrices-supercritical fluid extraction, pressurized fluid extraction and microwave-assisted extraction Their potential and pitfalls. Analyst 726 1182-1193. 

Microwave-assisted extractions (MAE) can be performed in open (focused MAE) or closed (pressurized MAE) flasks. This technique is commonly used for extractions from complex and difficult sample matrices, replacing time- and solvent-intensive Soxhlet extractions or hydrodistillations.46 MAE is also widely applied to environmental samples, for example, for extracting polycyclic aromatic hydrocarbons (PAH) from soil, methylmercury from sediments, and trace metals and pesticide residues from plant material47 48 The use of microwave treatment instead of hydrodistillation offers a solvent-free separation technique essential oils are heated and dry-distilled 46... 

Barriada-Pereira, M., M.J. Gonzalez-Castro, S. Muniategui-Lorenzo, et al. 2007. Comparison of pressurized liquid extraction and microwave assisted extraction for the determination of organochlorine pesticides in vegetables. Talanta 71 1345-1351. 

SC-C02 extraction modified by 10% ethanol is more efficient (Baumann et al., 2000), but the high operating pressure creates problems. Microwave-assisted extraction (MAE) technique for selective and rapid extraction of curcuminoids is also possible. 

Extraction procedures of plant materials classical percolation, maceration, digestion, decoction, and so on, as well as supercritical fluid extraction, microwave-assisted extraction, pressurized solvent extraction, and solid-phase microextraction are described. Eor biological matrices, liquid-liquid, and solid phase extractions are mainly used for different samples such as blood, urine, microdialysates, and saliva, among others. 

Keywords Pressurized liquid extraction supercritical fluid extraction ultra-sound-assisted extraction microwave-assisted extraction matrix solid-phase extraction high-performance liquid chromatography gas chromatography liquid-liquid extraction solid phase extraction column chromatography... 

A variety of solvent extraction techniques have been used to extract antioxidants from food matrices. The most commonly used is maceration or homogenization of the sample with an extraction solvent however, alternative procedures have been developed including pressurized fluid extraction (PFE), ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), and matrix solid-phase dispersion (MSPD), among others. The principles of each extraction technique will be briefly discussed. 

Novel sample preparation techniques include ultrasonic extractions that use high frequency acoustic waves to heat and break up samples (9), as well as microwave-assisted extractions (MAE) that use long wavelength radiation for faster and less energy intensive extractions of thermally sensitive analytes (JO-13). Other innovations treat samples with high pressure and high temperature solvents in the liquid or in the supercritical state. These adaptations reduce the overall solvent use and speed the extractions. These methods include accelerated solvent extraction (ASE) (14) and supercritical fluid extraction (SEE) (8). 

Fig. 5.5. (A) Scheme of a flow digestion system and the principle of pressure equilibration A pressure reactor, B heating zone, C cooling zone, D digestion coil, E cooling device, F connection for gas supply, G restrictor tube, H collector vial, I temperature sensor, J high-pressure pump, K injection valve, L sample loop, M sample, N and O peristaltic pumps. (Reproduced with permission of the American Chemical Society.) (B) Manifold for dynamic microwave-assisted extraction I solvent, 2 pump, 3 microwave oven, 4 extraction chamber, 5 temperature set-point controller, 6 thermocouple, 7 fluorescence detector, 8 recording device, 9 restrictor, 10 extractor. (Reproduced with permission of Elsevier.)...

Fig. 5.8. (A) General scheme of a dynamic focused microwave-assisted extractor. (B) Experimental set-up used to integrate microwave-assisted extraction with the subsequent steps of the analytical process. (1) Leaching step CT controller, MO microwave oven, S sample, R condenser, WR water reservoir, TCPP two-channel piston pump, ER extract reservoir, SV switching valve. (2) Clean-up/preconcentration step M methanol, A air, B buffer, PP peristaltic pump, F filter, EL elution loop, MC mini-column, R retention direction, E elution direction, 1V1-1V3 injection valves, W waste. (3) Individual separation-detection step HPIV high-pressure injection valve, AC analytical column, DAD diode array detector, SR solvent reservoirs.

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