Microwave-assisted extraction technique

Teo, C.C., Pool, W., Chong, K., Ho, Y.S. Development and application of microwave-assisted extraction technique in biological sample preparation for small molecule analysis. Metabolomics 9, 1109-1128 (2013)... 

The validation of the microwave-assisted extraction technique was performed by comparing the values obtained to that of the standard samples and by performing conventional prescribed official methods associated with each products under study. Table 2 presents a summary of data presented in references [19] and [20]. The results demonstrate that, in all cases, the microwave-assisted extraction procedures yielded data that were, for all practical purposes, similar to the accreditation values of fat content obtained for the same samples using conventional official methods. These results support the current trend whereby several microwave-assisted extraction methods are being evaluated for accreditation purposes. This trend is not exclusive to food analysis [27]. 

Tab. 22.3. Comparison of microwave-assisted extraction techniques for plant matrix. 

Theoretical and applied aspects of microwave heating, as well as the advantages of its application are discussed for the individual analytical processes and also for the sample preparation procedures. Special attention is paid to the various preconcentration techniques, in part, sorption and extraction. Improvement of microwave-assisted solution preconcentration is shown on the example of separation of noble metals from matrix components by complexing sorbents. Advantages of microwave-assisted extraction and principles of choice of appropriate solvent are considered for the extraction of organic contaminants from solutions and solid samples by alcohols and room-temperature ionic liquids (RTILs). 

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 recent years, extraction methods for PhACs have usually been based on liquid partitioning with ultrasonic extraction (USE) [43-47], microwave-assisted extraction (MAE) [48], or the more advanced PLE [49-52]. When compared to the other extraction techniques, PLE provides good recoveries, saves time and organic solvent, which makes it become currently a preferred technique for PhAC analyses. 

Lopez-Avila et al. [59] have described a microwave assisted extraction procedure for the separation of polyaromatic hydrocarbons from sediments. Tan [71] described a rapid sample preparation technique for analysing polyaromatic hydrocarbons in sediments. Polyaromatic hydrocarbons are removed from the sediment by ultrasonic extraction and isolated by solvent partition and silica gel column chromatography. The sulphur removal step is combined into the ultrasonic extraction procedure. Identification of polyaromatic hydrocarbon is carried out by gas chromatography alone and in conjunction with mass spectrometry. Quantitative determination is achieved by addition of known amounts of standard compounds using flame ionization and multiple ion detectors. 

Modem extraction and clean-up techniques, such as pressurised liquid extraction and microwave-assisted extraction, have almost not applied to the analysis of PFCs yet. Llorca et al. [49] reported the development and application of a PEE method for PFCs determination in fish. This technique provided rapid and accurately clean extracts for sensitive analysis. 

Microwave-assisted extraction (MAE) is a recent extraction technique, which combines microwave and traditional solvent extraction. The MAE approach have many advantages, such as shorter time, less solvent, higher extraction rate and better products with lower cost. Soxhlet... 

Microwave-assisted extraction (MAE) has been described for the extraction of various compounds from different matrices. It is a simple technique that can be completed in a few minutes. Microwave energy is applied to the sample suspended in solvent, either in a closed vessel or in an open cell. The latter allows larger amounts of sample to be extracted. A certain degree of heating is involved. 

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

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. 

Lopez-Avila et al. [107] showed that microwave-assisted extraction of pesticides and polycyclic aromatic hydrocarbons from soil is a viable alternative to Soxhlet extraction and needs a smaller sample volume and extraction time [108,109]. These techniques have also been compared in the case of chlorophenols. Lopez-Avila et al. compared microwave-assisted extraction with electron capture gas chromatography to ELISA for the determination of polychlorinated biphenyls in soils. Both techniques are applicable to field screening and monitoring applications. Microwave-assisted extraction [111, 112] and solid-phase microextraction [113] have been applied to the extraction of pesticides from soil. It was observed by these and other workers [114] that the selectivity of microwave-assisted extraction is highly dependent on the soil composition. 

Various other extraction techniques have been used to recover hydrocarbons from soil including microwave-assisted extraction [19] and supercritical fluid extraction coupled with on-line infrared spectroscopy detection [20,21], The on-line SFA infrared procedure produced results similar to those obtained by Soxhlet extraction. 

Other techniques that have been used to determine polycyclic aromatic hydrocarbons in soil extracts include ELISA field screening [86], micellar elec-tr okinetic capillary chromatography [ 87], supersonic jet laser-induced fluorescence [88,89], fluorescence quenching [90], thermal desorption gas chromatography-mass spectrometry [81,90,100], microwave-assisted extraction [91], thermal desorption [92], immunochemical methods [93,94], electrophoresis [96], thin layer chromatography [95], and pyrolysis gas chromatography [35]. 

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... 

This chapter covers techniques for the extraction of semivolatile organics from solid matrices. The focus is on commonly used and commercially available techniques, which include Soxhlet extraction, automated Soxhlet extraction, ultrasonic extraction, supercritical fluid extraction (SFE), accelerated solvent extraction (ASE), and microwave-assisted extraction (MAE). The underlying principles, instrumentation, operational procedures, and selected applications of these techniques are described. In a given application, probably all the methods mentioned above will work, so it often boils down to identifying the most suitable one. Consequently, an effort is made to compare these methodologies. 

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. 

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). 

In many situations, ultrasound-assisted leaching is an expeditious, inexpensive, efficient alternative to conventional extraction techniques and, in some cases, even to supercritical fluid and microwave-assisted extraction. A number of applications to both organic and inorganic analytes in a wide variety of samples exist. Most are conducted by hand. As with automatic extractions, applications involving continuous systems are still very scant and hence one possible target for future research. 

Ultrasound-assisted leaching has also been used to extract natural compounds such as vitamins A, D and E from feeds [57], paclitaxel and related taxoids from leaf tissue of Taxus [58], opiates from hair samples [59] and antioxidants from rosemary [60]. Ultrasounds have so far had much more restricted application in this field than in the previous ones, possibly as a result of the technique being at a disadvantage with respect to alternatives such as microwave-assisted extraction [57] or supercritical CO, extraction [60]. 

Although the traditional Soxhlet and solvent extraction techniques are widely accepted, they have inherent limitations and problems. Thus, Soxhlet extraction requires 12-24 h in most cases and uses high volumes of organic solvents (hundreds of millilitres). In contrast to conventional methods, microwave-assisted extraction can reduce the extraction time to less than 30 min and solvent consumption to under 50 ml [12]. Moreover, the recoveries obtained with microwave-assisted extraction are comparable with those provided by alternative extraction methods [7]. 

Microwave-assisted extraction (MAE) has become a major choice for the extraction of PCBs from solid matrices. In fact, this technique has been used to extract PCBs from a wide range of samples including soil, sediments and animal tissues [254-257], as well as certified reference materials (CRMs) [258]. Normally, the extractant used is the same as that employed with PAHs, viz. a 1 1 hexane-acetone mixture [246] however, organized media [256] have also provided results similar to those obtained with conventional methodologies such as Soxhlet extraction [259]. For example, the results for a range of Aroclors (1254, 1260, 1016 and 1248) were quite consistent with their certified values. The microwave-assisted extraction of PCB Aroclors 1248, 1254 and 1260 followed... 

The advantages of ASE over other techniques such as supercritical fluid extraction (SEE) and microwave-assisted extraction (MAE) are not so clear [16,60,62,116]. In fact, SEE features similar extraction times and uses little or no organic solvent. Also, SEE... 

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