Recovery microwave-assisted extraction

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. 

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] used microwave assisted extraction to assist the extraction of polyaromatic hydrocarbons from soils. Another extraction method was described by Hartmann [60] for the recovery of polyaromatic hydrocarbons in forest soils. The method included saponification of samples in an ultrasonic bath, partitioning of polyaromatic hydrocarbons into hexane, extract cleanup by using solid-phase extraction, and gas chromatography-mass spectrometric analysis using deuterated internal standards. Polyaromatic hydrocarbons were thermally desorbed from soils and sediments without pretreatment in another investigation [61]. 

Heise and Litz [26] investigated the extraction behaviour of surfactants (LAS, NPEO and cationics) from sand comparing Soxhlet extraction, accelerated solvent extraction (ASE) and microwave-assisted extraction. Fractionation of the three surfactant types anionic, non-ionic and cationic, was accomplished by column chromatography with aluminium oxide. Soxhlet extraction and ASE of spiked sand with methanol—stored during 7 days prior to extraction—gave similar recoveries for both LAS and NPEO with values between 88 and 116%. Less efficient extraction was achieved by microwave extraction (79% for NPEO). 

Supercritical fluid extraction (SFE), microwave-assisted extraction (MAE) and Soxhlet extraction under various experimental conditions were applied for spiked poly(vinyl) chloride samples. Extracted dyes were separated in an ODS column (250 X 4.6 mm i.d. particle size 5 jum) using methanol as the mobile phase. Dyes are well separated by this method as demonstrated in Fig. 3.59. The optimal parameters of the extraction methods are compiled in Table 3.23. Recoveries depended on both the type of extraction method and the chemical structure of the dye. It was found that the highest recovery can be obtained by MAE and the extraction efficacy was the lowest for Solvent red 24 [129],... 

OF samples were collected with the commercial device Salivette, which consists of a cotton swab that is inserted into the mouth for 2-3 min. Toxitubes A was compared to microwave assisted extraction (MAE). A volume of 1 ml of saliva was poured into each Toxitube and treated similarly as seen previously [109], For MAE different solvents (chloroform, dichloromethane, hexane), temperatures (80, 90, and 100 °C), and time periods (5, 10, and 15 min) have been tested finally 1 ml of saliva was mixed with 10 ml of chloroform and placed in the oven vessel for extraction at 100 °C for 10 min. Recoveries were found to range from 53 to 95 % with Toxitubes and from 83 to 100 % with MAE, so authors demonstrated that microwave-assisted extraction provides recoveries higher than those obtained for opiates with SPE. 

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]. 

Comparing microwave-assisted extraction (MAE) with ASE is as complicated as comparing the latter with SFE. In fact, the comparison cannot rely exclusively on recoveries as these are usually similar [30,62,73,114,116], so it must be made in other terms. For example, while ASE performs better than MAE and SFE in the extraction of hexa-conazole from aged contaminated soils — the more aged the soil, the better — [68], MAE is to be preferred to ASE for the extraction of hexachlorocyclohexane isomers from soils when expeditiousness is crucial (ASE allows up to 12 samples to be processed simultaneously, which results in substantially decreased total analysis times) [73]. 

The impact of the extraction conditions using various solvents on the recoveries has never been studied in detail, and the results have never been compared. The introduction of modern extraction methods, such as microwave-assisted extraction, supercritical fluid extraction, and solid-phase extraction, probably will improve the efficiency of extraction, even in the instance of unstable pigments and pigment mixtures. The majority of TLC separations were carried out on traditional silica layers. As the chemical structures and, consequently, the retention characteristics of pigments are highly different, a wide variety of eluent systems has been employed for their separation, consisting of light petroleum, ethyl formate, ethyl acetate, benzene, toluene, chloroform, methanol, n-butanol, formic or acetic acid, and so forth. 

A study was carried out for LEE by the Soxhlet method and microwave-assisted extraction for the determination of the priority phenols in soil samples. Recoveries varied from 67 to 97% with RSD between 8 and 14% for LEE, and >70% for the MAP, except for nitrophenols that underwent degradation when the latter method was applied. LOD was from 20 ngg for 2,4-dimethylphenol to 100 ngg for pentachlorophenol. The best detection method for EC was atmospheric pressnre chemical ionization MS (APCI-MS). The most abnndant ions obtained by this detection method were [M — H] for the lowly chlorinated phenols and [M — H — HCl] for tri-, tetra- and pentachlorophenols . 

As already observed for atmospheric microwave-assisted extraction (see Figure 7.13 above), it is found that the recoveries of polycyclic aromatic hydrocarbons from soil are similar irrespective of the extraction method used. In addition, similar precision is achieved in both cases. 

One of the first methods using microwave-assisted extraction of essential oil was presented in 1989 by Craveiro [44]. The essential oil of Lippia sidoides was extracted using microwave energy and compressed air only. Inspired by classical steam distillation, the CAMD technique used compressed air instead of vapor to extract the volatile oil. Typically, plant material is placed in a reactor inside the microwave cavity and heated. At the same time, a compressor, located outside the cavity, forces compressed air into the reactor. Volatile oil and vapor are then driven to the recovery flask outside the cavity. In 5 min CAMD provides an essential oil which is qualitatively and quantitatively identical with that produced by the conventional hydrodistillation method. 

Extraction, isolation and quantitation steps for POPs are summarized in Figure 1. Soxhlet extraction remains the method used by most analysts for recovery of chorinated pesticides and PCBs from sediments, and the one which other techniques such as shaking with solvent, ultrasonication, microwave assisted extraction, pressurized fluid extraction (PFE) and supercritical fluid extraction, are compared. 

Other extraction methods like (Ultra-Turrax) blending, ultrasonic, and solvent extractions are available. Most of these techniques show good recoveries for specific matrices, and after optimization of the extraction conditions. Microwave assisted extraction is another promising technique. Good recoveries for PCBs have been obtained. The extraction time is short, and samples can be extracted simultaneously. An overview of advantages and disadvantages of the various extraction techniques is given in Table 2. 

The commonly used extraction techniques for organotins are mechanical shaking, ultrasonic extraction, microwave-assisted extraction, or pressurized fluid extraction. Simple mechanical shaking has been used by many testing laboratories, but this has been generally shown to be less effective than the latter three techniques, particularly with respect to recoveries for monosubstituted species. One of the advantages of shaking or ultrasonication is that they... 

Test whether there are significant differences between (a) the concentration of chloride in the different solutions, and (b) the results obtained by the different methods. A new microwave-assisted extraction method for the recovery of 2-chlorophenol from soil samples was evaluated by applying it to five different soils on each of three days. The percentage recoveries obtained were ... 

The recovery of compour ds trapped inside the membrane is achieved by dialysis using an organic solvent such as hexane [97], cyclohexane [78,138], or by microwave-assisted extraction [149]. Setkova et al. give an overview of SPMD application for monitoring pollutants in various matrices [121]. 

The mode of extraction for PAHs is highly dependent on the matrix. For solid-based matrices such as food samples, sediments, soil, marine organisms, etc. extraction methods such as Soxhlet extraction with nonpolar solvent [35 6], hollow fiber membrane solvent microextraction (HFMSME) [10], pressimzed hquid extraction (PLE) [37,38], sonication extraction [3], microwave-assisted extraction (MAE) [3], supercritical fluid extraction, (SEE) [39], accelerated solvent extraction (ASE) [40], cold extraction [41], soxtec extraction [42], microwave-assisted alkaline saponification (MAAS) [43], dynamic microwave-assisted extraction (DMAE) [44], add-induced cloud point extraction (ACPE) [45], methanolic saponification extraction (MSE) [7], etc. are employed. Of all these, Soxhlet extraction is the most common for solid samples and has achieved excellent extraction with high-level recovery but its setback is the high consmnption of solvent and time associated with it. 

Microwave-assisted extraction was used to shorten sample preparation time for HPLC analysis. Results of determination were accurate in spite of the fact that sample grinding was omitted due to the novel method of extraction. In another study by HPLC, amides were extracted in a Soxhlet extractor from 3 cm wide strips, and excellent recovery was reported. Simultaneous determination of erucamide, oleamide, and stearamide was performed with good resolution, repeatability and reproducibility. ... 

MAE has also been used for the extraction of adipate plasticisers from PVC [464]. The efficiency of MAE depends on the kind of solvent, the temperature achieved and the heating time. The final temperature reached depends on the microwave power, number of vessels and irradiation time. Higher recovery values than SEE were reported for both phthalate and adipate. Other reports on microwave-assisted solvent extraction have appeared [465-467]. 

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