Ultrasound-assisted methods

Ultrasound-assisted methods are normally faster than those assisted by microwaves. 

Ultrasound-assisted methods are usually less robust than microwave-assisted ones because, as noted by Cencic-Kobda and Marcel [51], ageing of the US probe surface can alter the leaching efficiency. 

Mecozzi, M., Acquistucci, R., Amici, M., and Cardarilli, D., Improvement of an ultrasound assisted method for the analysis of total carbohydrate in environmental and food samples, Ultrason. Sonochem., 9, 219-223, 2002. 

Synthesis of aminooxazole derivatives via thermal and ultrasonic methods using deep eutectic solvent as the medium was recently reported by Singh et al. (2013). It was observed that the ultrasound-assisted method gave 90% yield in just 8 min as against 3.5 h required to achieve 69% yield by the thermal method. 2-Amino-4-aryloxazoles (80) were obtained via the reaction of phenacyl bromide derivatives (78) and amide derivatives (79) in a deep eutectic solvent (Scheme 8.25). The deep eutectic solvent used in this protocol was easily prepared from choline chloride (1 eq) and urea (2 eq) at 80°C by a previously reported method (Toukoniitty et al. 2006) with 100% atom economy. 

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]. 

Canals A, del Remedio HM (2002) Ultrasound-assisted method for determination of chemical oxygen demand. Anal Bioanal Chem 374(6) 1132-1140. doi 10.1007/s00216-002-1578-2... 

Diels-Alder Reaction Facilitated by Physical and Chemical Methods 155 Table 4.8 o-Quinone ultrasound-assisted Diels-Alder reactions... 

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 liquid-solid extraction (LSE) the analyte is extracted from the solid by a liquid, which is separated by filtration. Numerous extraction processes, representing various types and levels of energy, have been described steam distillation, simultaneous steam distillation-solvent extraction (SDE), passive hot solvent extraction, forced-flow leaching, (automated) Soxh-let extraction, shake-flask method, mechanically agitated reflux extraction, ultrasound-assisted extraction, y -ray-assisted extraction, microwave-assisted extraction (MAE), microwave-enhanced extraction (Soxwave ), microwave-assisted process (MAP ), gas-phase MAE, enhanced fluidity extraction, hot (subcritical) water extraction, supercritical fluid extraction (SFE), supercritical assisted liquid extraction, pressurised hot water extraction, enhanced solvent extraction (ESE ), solu-tion/precipitation, etc. The most successful systems are described in Sections 3.3.3-3.4.6. Other, less frequently... 

Some of the reports are as follows. Mizukoshi et al. [31] reported ultrasound assisted reduction processes of Pt(IV) ions in the presence of anionic, cationic and non-ionic surfactant. They found that radicals formed from the reaction of the surfactants with primary radicals sonolysis of water and direct thermal decomposition of surfactants during collapsing of cavities contribute to reduction of metal ions. Fujimoto et al. [32] reported metal and alloy nanoparticles of Au, Pd and ft, and Mn02 prepared by reduction method in presence of surfactant and sonication environment. They found that surfactant shows stabilization of metal particles and has impact on narrow particle size distribution during sonication process. Abbas et al. [33] carried out the effects of different operational parameters in sodium chloride sonocrystallisation, namely temperature, ultrasonic power and concentration sodium. They found that the sonocrystallization is effective method for preparation of small NaCl crystals for pharmaceutical aerosol preparation. The crystal growth then occurs in supersaturated solution. Mersmann et al. (2001) [21] and Guo et al. [34] reported that the relative supersaturation in reactive crystallization is decisive for the crystal size and depends on the following factors. 

Reisee et al. [52] first described a pulsed electrodeposition and pulsed out-of-phase ultrasound to prepare copper nanopowders. Such an electrochemical method has since then employed to synthesize a variety of nanoparticles. Mancier et al. [53] have prepared Cu20 nanopowders (8 nm) with very high specific surface area of 2,000 m2/g by pulsed ultrasound assisted-electrochemistry. 

High quality one-dimensional copper sulfide (CuS) nanorods (50-200 nm) have been demonstrated using template assisted electrochemical deposition, a sonoelec-trochemical method. Thus generated nanorods were also electrically characterized as p-type semiconductors [64]. In this process, ultrasound assists the electrochemical deposition by the combination of any of the following three processes ... 

Doping is important for semiconductors in order to tune their optical and electrical properties for the potential applications in biotechnology and solar cells [65]. Ag-doped hexagonal CdS nanoparticles were successfully obtained by an ultrasound-assisted microwave synthesis method. Here, the doping of Ag in to CdS nanoparticles induced the evolution of crystal structure from cubic to hexagonal. Further support from photocatalytic experiment also clearly indicates the doping of Ag clusters into the CdS matrix. 

Salim OM, Mahir I, Mahmut Bayramo glu (2005) Leaching of silver from solid waste using ultrasound assisted thiourea method. Ultrason Sonochem 12(3) 237-242... 

In the experiment involving oxidative enzyme HRP (EC 1.11.1.7, RZ 1.9, 240 purpuro gallin (units/mg)) [89] for the enzymatic treatment and ultrasonic waves of 423 kHz and 5.5 W, the phenol degradation rate was found to increase. The ultrasound assisted biodegradation method has been found to be more efficient method than the sonolysis and enzyme treatment when operated individually. 

Londono-Londono J, Rodrigues de Lima V, Lara O, Gil A, Pasa TBC, Arango GJ, Pineda JRR (2009) Clean recovery of antioxidant flavonoids from citrus peel optimizing an aqueous ultrasound-assisted extraction method. J Food Chem. doi 10.1016/j.foodchem.2009.05.075... 

Lavilla, I., P. Vilas, J. Millos, and C. Bendicho. 2006. Development of an ultrasound-assisted extraction method for biomonitoring of vanadium and nickel in the coastal environment under the influence of the Prestige fuel spill (North east Atlantic Ocean). Anal. Chim. Acta 577 119-125. 

Yue, X. Xu, Z. Prinyawiwatkul, W. King, J.M. 2006. Improving extraction of lutein from egg yolk using ultrasound-assisted solvent method. J. Food Sci. 71 C239-C241. 

Microwave and ultrasound assisted heating methods have the potential to overcome these problems via totally different calefaction processes. 

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. 

An important problem in this type of analysis is the presence of a matrix, the components of which hamper analysis by falsifying the results or generally making determination impossible. Therefore, in addition to developing appropriate methods of analysis, it is necessary to remove interferents and also to isolate and enrich analytes. For this purpose, various types of extractions are applied, usually LLE and SPE, but also others such as microextraction by packed sorbant (MEPS) and ultrasound-assisted emulsification microextraction (USAEME). 

Ultrasound-assisted slurry formation versus other sample preparation methods... 

Ultrasound-assisted emulsification in aqueous samples is the basis for the so-called liquid membrane process (LMP). This has been used mostly for the concentration and separation of metallic elements or other species such as weak acids and bases, hydrocarbons, gas mixtures and biologically important compounds such as amino acids [61-64]. LMP has aroused much interest as an alternative to conventional LLE. An LMP involves the previous preparation of the emulsion and its addition to the aqueous liquid sample. In this way, the continuous phase acts as a membrane between both the aqueous phases viz. those constituting the droplets and the sample). The separation principle is the diffusion of the target analytes from the sample to the droplets of the dispersed phase through the continuous phase. In comparison to conventional LLE, the emulsion-based method always affords easier, faster extraction and separation of the extract — which is sometimes mandatory in order to remove interferences from the organic solvents prior to detection. The formation and destruction of o/w or w/o emulsions by sonication have proved an effective method for extracting target species. 

Ultrasound-assisted electrolytic reduction of emulsions of activated unsaturated systems provides a method for hydrogenation of water-insoluble materials in an aqueous environment [284]. The effect of ultrasound on electrochemical reactions in emulsions may vary depending on the reaction in some cases solubilization of an insoluble reaction product is furthered, whereas in other cases the heterogeneous rate constant is influenced [284]. 

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