Ultrasound spectrometry

Before we discuss the applications of US-based detection techniques, we should emphasize the difference between the measured data and the desired output parameters. In ultrasound spectrometry, the measured data can be the attenuation coefficient, the sound speed and the acoustic impedance. However, the researcher is rarely interested in these measured properties, but rather on elastic moduli of solid samples particle size distributions or rheological properties of heterogeneous samples and concentrations, rheology, stability and chemical reactivity of liquids (particularly emulsions). 

Analytical uses of ultrasound spectrometry in homogeneous solutions... 

The kinetics of formation and disintegration of micelles has been studied for about thirty years [106-130] mainly by means of special experimental methods, which have been proposed for investigation of fast chemical reaction in liquids [131]. Most of the experimental methods for micellar solutions study the relaxation of small perturbations of the aggregation equilibrium in the system. Small perturbations of the micellar concentration can be generated by either fast mixing of two solutions when one of them does not contain micelles (method of stopped flow [112]), or by a sudden shift of the equilibrium by instantaneous changes of the temperature (temperature jump method [108, 124, 129, 130]) or pressure (pressure jump method [1, 107, 116, 122, 126]). The shift of the equilibrium can be induced also by periodic compressions or expansions of a liquid element caused by ultrasound (methods of ultrasound spectrometry [109-111, 121, 125, 127]). All experimental techniques can be described by the term relaxation spectrometry [132] and are characterised by small deviations from equilibrium. Therefore, linearised equations can be used to describe various processes in the system. 

Also known for some time is a phase transition at low temperature (111K), observed in studies with various methods (NQR, elasticity measurement by ultrasound, Raman spectrometry) 112 temperature-dependent neutron diffraction showed the phase transition to be caused by an antiphase rotation of adjacent anions around the threefold axis ([111] in the cubic cell) and to lower the symmetry from cubic to rhombohedral (Ric). As shown by inelastic neutron scattering, this phase transition is driven by a low-frequency rotatory soft mode (0.288 THz 9.61 cm / 298 K) 113 a more recent NQR study revealed a small hysteresis and hence first-order character of this transition.114 This rhombohedral structure is adopted by Rb2Hg(CN)4 already at room temperature (rav(Hg—C) 218.6, rav(C—N) 114.0 pm for two independent cyano groups), and the analogous phase transition to the cubic structure occurs at 398 K.115... 

For the last several years, mass spectrometry with atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) have determined the trends in the analysis of dyes. Since 1987, various variants of ESI have been used in which droplet formation was assisted by compressed air,[1,2] temperature (e.g. Turbo Ion Spray ) or ultrasound, and they were able to handle flow rates up to 1 2 ml min This made a combination of analytical RPLC and ESI easily and widely used. The reason why it often was (and is) used instead of a traditional UV-Vis detector is the better sensitivity and selectivity of MS in comparison with spectrophotometric detection. Apart from these advantages, MS offers easily interpretable structural information. However, various... 

M. C. Yebra and S. Cancela, Continuous ultrasound-assisted extraction of cadmium from legumes and dried fruit samples coupled with on-line preconcentration-flame atomic absorption spectrometry, Anal. Bioanal. Chem., 382(4), 2005, 1093-1098. 

A. Moreno-Cid and M. C. Yebra, Flow injection determination of copper in mussels by flame atomic absorption spectrometry after on-line continuous ultrasound-assisted extraction, Spectrochim. Acta, Part B, 57(5), 2002, 967-974. 

F. Priego-Capote and M. D. Luque-de-Castro, Dynamic ultrasound-assisted leaching of essential macro and micronutrient metal elements from animal feeds prior to flame atomic absorption spectrometry. Anal. Bioanal. Chem., 378(5), 2004, 1376-1381. 

C. Pena-Farfal, A. Moreda-Pineiro, A. Bermejo-Barrera, P. Bermejo-Barrera, H. Pinochet-Cancino and I. De-Gregori-Henriquez, Ultrasound bath-assisted enzymatic hydrolysis procedures as sample pretreatment for multielement determination in mussels by inductively coupled plasma atomic emission spectrometry, Anal. Chem., 76(13), 2004, 3541-3547. 

An application of ultrasound that is becoming increasingly popular in the food industry is the determination of creaming and sedimentation profiles in emulsions and suspensions (Basaran et al., 1998). Acoustic techniques can also assess nondestructively the texture of aerated food products such as crackers and wafers. Air cells, which are critical to consumer appreciation of baked product quality, are readily probed due to their inherent compressibility (Elmehdi et al., 2003). Kulmyrzaev et al. (2000) developed an ultrasonic reflectance spectrometer to relate ultrasonic reflectance spectra to bubble characteristics of aerated foods. Experiments were carried out using foams with different bubble concentration and the results showed that ultrasonic reflectance spectrometry is sensitive to changes in bubble size and concentration of aerated foods. 

Fernandez, C., A.C.L. Conceicao, R. Rial-Otero, C. Vaz, and J.L. Capelo. 2006. Sequential flow injection analysis system on-line coupled to high intensity focused ultrasound Green methodology for trace analysis applications as demonstrated for the determination of inorganic and total mercury in waters and urine by cold vapor atomic absorption spectrometry. Anal. Chem. 78 2494-2499. 

Vaisainen, A. and R. Suontomo. 2002. Comparison of ultrasound-assisted extraction, microwave-assisted acid leaching and reflux for the determination of arsenic, cadmium and copper in contaminated soil samples by electrothermal atomic absorption spectrometry. J. Anal. At. Spectrom. 17 739-742. 

Gil, S., I. Lavilla, and C. Bendicho. 2006. Ultrasound-promoted cold vapor generation in the presence of formic acid for determination of mercury by atomic absorption spectrometry. Anal. Chem. 78 6260-6264. 

Orozco-Solano, M. Ruiz-Jimenez, J. Luque de Castro, M.D. 2010. Ultrasound-assisted extraction and derivatization of sterols and fatty alcohols from olive leaves and drupes prior to determination by gas chromatography-tandem mass spectrometry. J. Chromatogr. A 1217 1227-1235. 

Magiera, S., Giilmez, S. Ultrasound-assisted emulsification microextraction combined with ultra-high performance liquid chromatography-tandem mass spectrometry for the analysis of ibuprofen and its metabolites in human urine. J. Pharm. Biomed. Anal. 92, 193-202 (2014)... 

Part II of the book deals with lesser known aspects of US for the analytical chemists such as its use as an energy source for detection purposes. Thus, ultrasound-based detection techniques viz. US spectrometry in its various modes including ultrasound attenuation, ultrasonic velocity, resonant ultrasound, laser-generated, ultrasound reflection and acoustic wave impedance spectroscopies) are dealt with in Chapter 9. Finally, Chapter 10 is devoted to seleoted applioations of US spectrometry — mostly non-analytical applications from whioh, however, analytical chemists can derive new, interesting analytical uses for ultrasound-based deteotion techniques. 

As with any analytical technique, it is important for US spectrometry users to have a thorough understanding of its underlying physical principles and of potential sources of errors adversely affecting measurements. The basis of ultrasonic analyses in a number of fields (particularly in food analysis) is the relationship between the measurable ultrasonic properties (velocity, attenuation and impedance, mainly) and the physicochemical properties of the sample (e.g. composition, structure, physical state). Such a relationship can be established empirically from a calibration curve that relates the property of interest to the measured ultrasonic property, or theoretically from equations describing the propagation of ultrasound through materials. 

Ultrasound-assisted sample preparation in flow analysis is a relatively recent approach and the number of applications is much lower than those using microwave or UV radiation [145]. In general, a relatively long sonication time is needed. As mild conditions are involved, this approach has been more exploited in combination with atomic absorption/emis-sion spectrometry and related techniques, as the partially prepared samples are more compatible with these techniques (see above). Apart from sample solubilisation/digestion, there are other potential applications ... 

Hydride generation, as demonstrated by the determination of toxic arsenic species in human urine by cold-vapour atomic absorption spectrometry [148]. Two advanced oxidation processes relying on high-intensity focussed ultrasound were compared and ultrasound played an important role in both. Accurate results were reported. 

A. Correia, M. Galesio, H. Santos, R. Rial-Otero, C. Lodeiro, A. Oehmen, A.C.L. Conceicao, J.L. Capelo, Can sample treatments based on advanced oxidation processes assisted by high-intensity focused ultrasound be used for toxic arsenic determination in human urine by flow-injection hydride-generation atomic absorption spectrometry Talanta 72 (2007) 968. 

The thermoelastic behavior of micas was also studied by dynamic methods, namely shock wave compression (Sekine et al. 1991), or by techniques involving resonant ultrasound spectroscopy (Aleksandrov and Ryzhova 1961) or by Brillouin spectrometry (Vaughan and Guggenheim 1986). 

Organotin compounds have also been determined in house dust (Fromme et al. 2005) (see Table 3). Ultrasound-assisted extraction (USAE) was conducted with ethanol, followed by derivatization with sodium tetraethylborate (STEB) and liquid-liquid extraction with n-hexane. Extracts were analysed by gas chroma-tography/mass spectrometry. Recoveries higher than 70% and average LODs of 10 ng g were obtained. 

Cortada, C. Vidal, L. Canals, A. (2011). Determination of geosmin and 2-methyhsobomeol in water and wine samples by ultrasound-assisted dispersive hquid-liquid microextraction coupled to gas chromatography-mass spectrometry. Journal of Chromatography A1218,17-22... 

Fontana, R, Patd, S., Banerjee, K., Altamirano, J. (2010). Ultrasound-Assisted Emulsification Microextraction for Determination of 2,4,6-Trichloroanisole in Wine Samples by Gas Chromatography Tandem Mass Spectrometry. /. Agric. Food Chem., Vol.58, N°8, pp. 4576-4578, ISSN 15205118. 

Reversed-phase high-performance liquid chromatography Scoville heat unit Solid-phase micro extraction Ultrasound-assisted extraction Ultra-high-performance liquid chromatography Ultra-performance liquid chromatography combined with mass spectrometry Ultraviolet... 

Chen F, Sun Y, Zhao G, Liao X, Hu X, Wu J, Wang Z (2007) Optimization of ultrasound-assisted extraction of anthocyanins in red raspberries and identiflcation of anthocyanins in extract using high-performance liquid chromatography-mass spectrometry. Ultrason Sonochem 14(6) 767-778... 

Bianco A, Uccella N (2000) Biophenolic components of olives. Food Res Int 33 475 85 Savarese M et al (2007) Characterization of phenolic extracts from olives (Olea europaea cv. Pisciottana) by electrospray ionization mass spectrometry. Food Chem 105 761-770 Ryana D et al (1999) Determination of phenolic compounds in olives by reversed-phase chromatography and mass spectrometry. J Chromatogr A 832 87-96 Priego-Capote F et al (2004) Fast separation and determination of phenolic compounds by capillary electrophoresis-diode array detection application to the characterization of alperujo after ultrasound-assisted extraction. J Chromatogr A 1045 239-246... 

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