Microwave-assisted extraction procedures

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. 

Lopez-Avila et al. [23] have described a microwave assisted extraction procedure for the separation of chlorinated insecticides from sediments. 

Khajeh, M. Optimization of microwave-assisted extraction procedure for zinc and copper determination in food samples by Box-Behnken design. J. Food Compos. Anal. 22, 343-346 (2009)... 

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]. 

Table 9. Microwave-assisted extraction procedures used in the monitoring of PAHs in air. ...

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). 

Table 3.10 shows the recovery from PP of Irgafos 168 and its oxidised and hydrolysed by-products by various extraction procedures. As may be observed, One-Step Microwave-Assisted Extraction (OSM) and US lead both to negligible hydrolytic additive degradation. The measured additive decay (by oxidation) is essentially due to the antioxidant activity during the processing (extrusion) step of the polymer and not to the US or microwave heating treatment. 

Fig. 3.71. Flow scheme for the analytical procedure based on microwave-assisted extraction (MAE). Reprinted with permission from C. S. Eskilsson et al. [140].

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. 

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. 

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. 

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. 

Microwave-assisted extraction has also been used as a solid sample treatment prior to speciation analysis [264-266], leaving the organometallic compound moiety intact. This is a prerequisite for a successful extraction procedure to be applied prior to speciation analysis and can be met by careful optimization of the conditions of the microwave attack. Open-vessel treatment is preferred to pressurized bomb systems commonly used in the analysis for total metals because it offers milder reaction conditions — the increase in temperature is governed to a great extent by the boiling point of the solvent — and easier control of process variables [266]. 

An increasing demand for new extraction techniques, susceptible to automation, with shorter extraction times and reduced solvent consumption, giving reduced sample preparation costs and preventing pollution in laboratories, has been seen in recent decades. This progress in sample preparation has resulted in new techniques such as microwave assisted extraction (MAE), supercritical fluid extraction (SEE) and accelerated solvent extraction (ASE). These techniques are similar in that they involve working at elevated temperatures and pressures, which improves the speed of the extraction procedure. 

The examples described in this section 10.6.1 constituted the first report ever of ill situ reaction-extraction work involving foodstuffs. We had reported earlier on a related approach in a different field, namely a derivatisation-extraction procedure whereby phenols and methylated phenols were acetylated-extracted from environmental matrices in a one-step MAP procedure (15). The latter procedure, however, was performed under much harsher conditions that could not be used with foodstuffs where the potential of creating artefacts is a prime concern. This approach of one-pot, multiple-step procedures opens the avenue to numerous applications of direct interest to the food analysts and are especially versatile and valuable when using microwave-assisted extraction performed in open-vessel systems. This, along with solvent-less extraction (such as MAP gas-phase applications ) is believed... 

Figure 7.12 Typical procedure used for the microwave-assisted extraction of solids.

A typical procedure used for microwave-assisted extraction is shown in Figure 7.12. 

To date, little work has been cited in the literature with respect to arsenic speciation of polluted soil. A feasibility study on the identification and monitoring of arsenic species in polluted soil and sediment samples (Thomas etal. 1997) has been reported. In this study, polluted soil samples were extracted in phosphoric acid media using an open vessel microwave-assisted extraction system. The determination of arsenic species was investigated using an on-line system involving HPLC-ICP-MS system. The speciation was performed to identify As(III), As(V) and monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). The proposed method had the potential to form the basis of a routine procedure for monitoring the behaviour of arsenic species in soils. This extraction procedure was recently applied to contaminated... 

Even though the interest in microwave-assisted extraction (MAE) has increased during the last 10 years, this technique has not been utilized much in food and feed applications. Only a few papers can be found with the combination of POPs and food/feed samples. This may be because MAE applications frequently require laborious and tedious clean-up of the extracts before final analysis. In some cases, only a simple filtration or centrifugation may be sufficient to separate the solid matrix from the extract but since MAE most often is more exhaustive than selective, extensive clean-up procedures based on for example solid-phase extraction is commonly needed for removal of interfering compounds (73-75). Other techniques that have been used for clean-up of MAE extracts are gel permeation chromatography (75), solid-phase micro extraction (77, 78), and liquid-liquid extraction (79). 

The procedure to be used to extract carbamate pesticides from environmental samples depends on their polarity and on the type of sample matrix involved. Various choices exist for the extraction of pesticides ranging from conventional procedures (e.g., Soxhlet extraction, liquid-liquid extraction (LLE), evaporation, steam distillation) to new methodologies including solid-phase extraction (SPE), solid-phase microextraction (SPME), supercritical fluid extraction (SEE), matrix solid-phase dispersion (MSPD), accelerated solvent extraction (ASE) and microwave-assisted extraction. " ... 

Many procedures report the contribution of ultrasounds or microwaves to quantitatively extract the trapped compounds. For example, a low temperature microwave-assisted extraction method (MAE) was reported to determine PAHs in airborne particulate matter (Karthikeyan et al. 2006). The procedure requires a... 

Various sample preparation approaches, including microwave-assisted extraction and enzymatic digestion procedures, were examined to extract selenium from the defatted Brazil nut matrix among these approaches, enzymatic treatment with Proteinase K proved most effective [49]. SeMet was demonstrated to be the most abundant of these seleno-amino acids. In their study, another selenium species with m/z = 361 was also detected. By application of collision-induced dissociation (CID), there was evidence for this compound to be a dipeptide consisting of tyrosine and methionine with Se [49] as shown in Figure 9.1. It was proposed by the authors that this was a dipeptide with the structure p-HO(QH4)CH2CH(NH2)CONHCH(COOH)CH2CH2SeCH3. 

Other analytical procedures, such as supercritical fluid extraction (SFE) and microwave-assisted extraction (MAE), are gaining significant attention. SFE is commonly applied to many analyses that require extraction from solid matrices and has found important applications in the... 

Scheme 5.1 A protocol for sample preparation prior to chiral analysis of the pollutants. Note that this is only a brief outline of the sample preparation procedure. MAE, microwave assisted extraction SE, Soxhlet extraction ASE, accelerated solvent extraction SFE, solid phase extraction CC, column chromatography HPLC, high performance liquid chromatography SFC, supercritical fluid chromatography GPC, gel permeation chromatography.

To manage a sufficient detection it is essential to extract almost quantitatively PAHs from complex matrices -such as bivalves- and minimize interferences. Simplified procedures for the analysis of PAHs in mussels have been reported by various groups whose primary aim was the optimization of GC-MS methods (Martinez et al. 2004). Indicatively Navarro et al. assessed different clean-up procedures used in the determination of PAHs in biota samples such as oysters and mussels (Navarro et al. 2006). Briefly the extraction of PAHs was pursued by (a) Microwave assisted saponification (MAS) (b) Microwave assisted extraction (MAE) and their clean up by SPE and GPC. 

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