recent applications for high-resolution ultrasonic spectroscopy

Breda O'Driscoll, Cormac Smyth, Arno C. Alting, Ronald W. Visschers, Vitaly Buckin

American Laboratory, February, pp. 54-57 (2003)

High-resolution ultrasonic spectroscopy is a novel technique for material analysis based on the measurements of parameters of ultrasonic waves propagating through samples. It allows direct and nondestructive measurements of intrinsic properties of materials, without formation of derivatives or changing their state. Originally, spectroscopy was considered mainly to be the study of electromagnetic radiation with matter. Later, MS was added due to its very high resolution and discriminating ability for chemicals. However, sound also interacts with matter. Matter can absorb the sound, which attenuates the signal, or it can change the velocity of the signal. As most materials are transparent, the analyzed sample can be highly colored or even opaque to light. Ultrasound spectroscopy has expanded the range of spectroscopic tools for characterization of chemical and physical mixtures.

The family of ultrasonic spectrometers discussed here, the HR-US range (Ultrasonic Scientific, Dublin, Ireland), has provided the international laboratory community with an analytical technique that is suitable for an almost limitless range of applications. First featured in the March 2002 issue of American Laboratory, 1 the instrument has won the Silver Award at the 2002 Pittsburgh Conference (New Orleans, LA, March 2002) and an R&D Top 100 Award. A schematic of instrumentation for high-resolution spectroscopy is illustrated in Figure 1. Ultrasonic spectroscopy measures the change in velocity and attenuation of the ultrasonic wave caused by interaction of sound with the components of the sample. Most frequently, sound attenuation is measured, since this is simple and not temperature sensitive. Attenuation and velocity are sensitive to changes in intermolecular interactions and molecular organization. Most commonly, the measurement is made in a cuvette with a volume of 1 mL. Typical applications of attenuation measurements include kinetics of fast reactions and particle sizing in emulsions and suspensions. In contrast, velocity changes are a measure of the microelasticity of the analytes., compared to reference (unfortified) skim milk. Fortification with calcium reduces the stability of the casein micelles, which lowers the coagulation temperature.

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