Ultrasound extraction efficiency

In order to increase the overall extraction efficiency during SFE sonication has been applied [352]. Ultrasound creates intense sinusoidal variations in density and pressure, which improve solute mass transfer. Development of an SFE method is a time-consuming process. For new methods, analysts should refer the results to a traditional sample preparation method such as Soxhlet or LLE. 

The UAE technique is based on the employment of the energy derived from ultrasounds that facilitate the extraction of analytes from the solid sample by the organic solvent [66]. The enhancement of extraction efficiency of organic compounds by UAE is attributed to the phenomenon of cavitation produced in the solvent by the passage of ultrasonic waves [67]. The uses of higher temperatures in UAE lead to an increase in the efficiency of the extraction process [67-69]. The ultrasound-assisted extraction of capsaicinoids from pepper has also been carried out by Barbero et al. in... 

With liquid samples as oils, OL isolation has been realized by two main techniques liquid-liquid extraction (LLE) and solid-phase extraction (SPE) [14, 73]. LLE is based on transfer of the phenolic fraction from VOO to a more hydrophilic phase such as pure methanol or methanol-water mixtures with different alcohol concentrations [42 14]. Ultrasounds can be used as auxiliary energy to accelerate and improve LLE. The main advantages of ultrasound-assisted LLE are shortened extraction time, reduced reagent and sample volume, and improved extraction efficiency [32, 48]. After extraction, cleanup and pre-concentration steps are... 

Ionic liquid-based ultrasound-assisted extraction (ILUAE) was successfully applied to the extraction of three alkaloids, vindoline, catharanthine, and vinblastine from Catharanthus roseus. Twelve ionic liquids, with different cations and anions were investigated in this work. In addition, ultrasound extraction parameters, including soak time, solid-liquid ratio, ultrasound power and time, and the number of extraction cycles, were optimized. ILUAE offered short extraction times (from 0.5 to 4 h) and remarkable efficiency. Therefore, the use of ionic hquids in the ultrasound-assisted extraction of key chemicals from medicinal plants shows great potential [12]. 

The use of auxiliary energies to accelerate or increase the extraction efficiency of OBPs from OIW has scarcely been explored even though ultrasound and superheated extractants have been found to result in improved extraction. An attempt to extract BPs from alpemjo was made by using the continuous ultrasound-assisted method based on the approach illustrated in Figure 4.11, where the sample, held in the extraction chamber, was subjected to the action of an ultrasound probe meanwhile, the extractant (1 3 methanol-water) was recirculated in a closed circuit to ensure adequate mass transfer to the liquid phase under optimal working conditions. The direction of the extractant was changed at 40 s intervals to minimize dilution of the extract and compaction in the extraction cell, which could result in overpressure in the dynamic system [268]. 

Ultrasound has also been used to enhance extraction of oil from oilseed rape (Wei et al., 2008). As with other studies, extraction efficiency was significantly affected by extraction time and extraction power, and then the liquidisolid ratio. A liquidisolid ratio of 1 4 (L g), an ultrasound-assisted extraction time of 60 min, and power of 500 W were found to be optimal for extracting up to 20 mg of ground oilseed rape, when compared to a standard Soxhlet extraction method. 

Ultrasound-assisted extraction provides efficient extraction in a shorter processing time than is needed for conventional extraction. The aid of ultrasound will result in a higher extraction yield and reduce solvent consumption. The extract may exhibit a wide range of colors (pale yellow, brown, red). For anthocyanin extraction in an acidic environment, the extract will be deep red, pink, or purple. The extract may contain considerable amounts of lipophilic compounds (e.g., chlorophyll, carotenoids, lipids). Prior to solid-phase extraction, those compounds can be eliminated from the extracts using liquid-liquid extraction. 

Acetonitrile, acetone, ethanol, and methanol have been used to extract isoflavones from soy foods. Among them, acetonitrile proved to be the most efficient (Griffith et al., 2001 Murphy et al., 2002). The solvent is supplemented with 0.1 M HC1 to completely un ionize the isoflavones and to release them from protein complexes by denaturing and precipitating the proteins. Room temperature is recommended for extraction to avoid alteration of the natural forms of the isoflavones. The time for extraction, 2 hr, was chosen for maximum recovery and shortest processing time. Ultrasound is used to aid the extraction process by degrading and weakening the cellular matrix. 

Ultrasound-assisted extraction (USE) is an effective method for leaching many analytes from different kinds of samples [52-55]. It is simple, fast, efficient, and inexpensive in comparison with conventional extraction techniques such as solvent extraction in the Soxhlet apparatus. Ultrasound-assisted solid-liquid extraction is an effective and time-saving extraction method. Sonication accelerates the mass-transfer process between two phases. Use of ultrasound results in a reduction in operating temperature, allowing the extraction of temperature-sensitive components. The ultrasound apparatus is cheaper and its operation is easier in comparison with other novel extraction techniques such as MAE. 

There are many review articles concerning application of USE in food technology [57] and for isolation of bioactive substances from herbs and other plant materials [58], as well as leaching of heavy metals from environmental and industrial samples [59]. Application of ultrasound during sequential extraction of trace elements significantly shortens the whole procedure however, for satisfactory efficiency it is necessary to increase the temperature and modify the matrix. 

Another example of ultrasound use is leaching of organic impurities from different kinds of samples. The main analytes of interest are PAHs, which are widespread in soil, sediment, dust, and particulate samples [55]. USE is recommended as a fast, efficient, and direct environmental sample preparation method for determination of PCBs, nitrophenols, pesticides, or polymer additives. Organometallic and biologically active compounds (such as vitamins A, D, and E) present in samples in trace quantities, can be extracted from animal and plant tissues with the aid of ultrasonic wave energy [59]. Table 6.6 presents some typical applications of USE in trace analysis of biological and environmental samples [60]. 

A higher methanol content in the extraction mixture enhances the effectiveness of extraction of organic arsenic derivatives without altering the effectiveness of release of As(III) and As(V) salts, and arsenosugars [89]. The duration of the process can be reduced by ultrasound treatment or pressurized extraction [90]. Multiple extraction does not improve the efficiency of the process the quantity of arsenic remaining in the solid material depends solely on the volume of solvent retained in it (usually in the first cycle) and not on the number of repetitions of the leaching process [91]. 

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. 

Ultrasonic extraction is especially efficient with environmental and industrial hygiene samples however, in addition to the inapplicability to the extraction of some metals and the inability to quantitatively extract heavy metals from very large bulk environmental samples [14,15], ultrasounds occasionally produce ionic species that were absent from the original sample. The new species give unidentified signals that yield spurious analytical results such is the case with the extraction of ionic species from airborne particulate matter [23], where the new ions formed prevent accurate determination of those initially present in the sample. 

One other major group of pollutants for which ultrasound-assisted leaching is an effective extraction method is that of polychlorinated biphenyls (PCBs) [43-45]. Their persistence and accumulation in the environment has led to their inclusion in monitoring programme analyses. In most cases, ultrasonic extraction is recommended as a fast, efficient, straightforward choice for these compounds, particularly in routine analyses [44]. 

The isolation of the effective compositions from some traditional Chinese herbs under influence of ultrasound was reported [71], The compounds Helicid (4-for-mylphenyl-allopyranoside), Berberin Hydrochloride, and Bergenin could each be isolated from different plant materials using ethanol at room temperature under the influence of sonication. Ultrasonic irradiation reduced the temperature and time required for the process, thereby increasing the efficiency of extraction. The products contained fewer impurities and the ultrasonic process appeared to involve simpler technology. 

The extraction of tea leaf solids with water under the influence of ultrasound has been studied with respect to the effects of temperature, irradiation time, and power [72], Sonication improved the extraction at 60 °C by nearly 20%, approaching the efficiency of that of thermal extraction at 100 °C. 

The Coventry group has also examined the behavior ofp-chlorophenyl acetate electrooxidation under ultrasound [187]. This substrate is known to markedly favor the two-electron mechanism [180], showing that the choice of reaction pathway is more dependent on substrate nature than upon manipulation of electrolysis parameters. A further feature of this system is the appreciable yield of p-chlorobenzalde-hyde-derived products. This is shown in Table 6 where it can be seen that sonication produces little change in relative product ratio, although there is an increase in total yield after ether extraction. Thus 46% by weight of mixed product is obtained (unreacted acid is not recovered by this procedure) with ultrasound, but only 23% by weight from the silent reaction. This represents increased reaction efficiency since the same quantity of charge was passed in each case. 

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