The Sound of Compounds

摘要

With the right application, photoacoustic spectroscopy is a chemist's dream. It began with Alexander Graham Bell's cigar smoke, so the story goes. On a cloudy day in Paris in the 1880s, a beam of sunlight filtered through, hit a glass tube filled with cigar smoke, and generated musical tones. Today, scientists apply the same photoacoustic (PA) technique to determine Aspergillus flavus, a toxic corn fungus, and to noninvasively measure blood glucose levels. While photoacoustic spectroscopy (PAS) is fast, sensitive, nondestructive, and selective and has a wide dynamic range, Murty Neti of California Analytical Instruments remarks that the technique in the United States was "more or less a lab curiosity," at least through the 1970s. In some respects, PAS is a chemist's dream. Most analytical techniques require some sample preparation, but John McClelland of MTEC Photoacoustics says that PAS "allows you to just toss them into a sample holder and measure their [PAS] absorption." Depending on the instrument, PAS can analyze almost any physical state, whether the material is shiny, transparent, opaque, or light scattering. Samples can be quite small and analyzed qualitatively, or they can be quantitatively compared with known reference standards.