Sampling solids ultrasound-assisted

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... 

M. C. Yebra, A. Moreno-Cid, R. Cespon and S. Cancela, Preparation of a soluble solid sample by a continuous ultrasound assisted dissolution system for the flow-injection atomic absorption spectrometric determination of iron in milk powder and infant formula, Talanta, 62(2), 2004, 403 406. 

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. 

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. 

As noted earlier, some of the steps that precede the insertion of the treated sample into the instrument for measurement (e.g. dissolution, clean-up, preconcentration, individual separation, derivatization) can have a critical influence on accuracy and precision depending on the particular step. All analytical processes include a sample preparation step which is a function of a number of factors such as the physical state of the sample, the nature of the sample matrix and analytes or the type of detector, for example. The first distinction therefore refers to the nature of the sample solid, liquid or gas. Solid samples are the most difficult to process as most analytical instruments cannot handle them. Therefore, the first operation in solid sample preparation involves transferring the target analytes to a liquid phase. This can be carried out in various ways including total dissolution of the test sample or partial dissolution or separation of a portion thereof. The different choices, which can be assisted by ultrasound, are depicted in Fig. 2.2, and discussed in the following sections. 

Misused terms in relation to ultrasound-assisted solid sample pretreatment... 

Ultrasound-assisted dissolution of the solid phase in heterogeneous samples... 

Fig. 3.7. Approaches to implementing continuous ultrasound-assisted leaching. (A) With direct monitoring of the process. (B) and (C) With a derivatization step before detection. (Bl) With leaching in the recirculation mode. (Cl) With leaching in the go forward and back mode. (B2) and (C2) Derivatization-detection steps. P peristaltic pump, UP ultrasound probe, SS solid sample, DB de-bubbler, D detector, SV switching valve, LC leaching carrier, R reagent, W waste. (Reproduced with permission of Elsevier.)...

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... 

Barfi, B., A. Asghari, M. Rajabi, A. Barfi, and I. Saeidi. 2013. Simplified miniaturized ultrasound-assisted matrix solid phase dispersion extraction and high performance liquid chromatographic determination of seven flavonoids in citrus fruit juice and human fluid samples Hesperetin and naringenin as biomarkers, f. Chromatogr. A 13H(l) 30-40. 

Figure 13. Scheme of steps involved in a micellar microwave- or ultrasound-assisted extraction to determine PAHs in solid samples. 

Ultrasounds have been used to assist in the insertion of samples into solid-liquid analytical systems for some time. The earliest ultrasonic nebulizers and automatic slurry sampling systems were reported in the 1980s. However, the actual potential of ultrasounds for increasing the efficiency of sampling systems remains to be explored. Thus, a recently developed technique based on acoustic levitation has been found to substantially... 

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