Analytical Chem istry - DePauw University

392 Analytical Chemistry 2.0(a)(b)(c)(d)Figure 8.13 Four possible mechanisms for the solid-state extraction of an analyte:(a) adsorption onto a solid substrate; (b) absorption into a thin polymer film orchemical film coated on a solid substrate; (c) metal–ligand complexation in whichthe ligand is covalently bound to the solid substrate using an organic tether; and(d) antibody–antigen binding in which the receptor is covalently bound to thesolid substrate using an organic tether.If you own a wristwatch, there is a goodchance that its operation relies on a quartzcrystal. The piezoelectric properties ofquartz were discovered in 1880 by Paul-Jacques Currie and Pierre Currie. Becausethe oscillation frequency of a quartz crystalis so precise, it quickly found use inthe keeping of time. The first quartz clockwas built in 1927 at the Bell Telephonelabs, and Seiko introduced the first quartzwristwatches in 1969.Another method for extracting an analyte from its matrix is by adsorptiononto a solid substrate, by absorption into a thin polymer or chemicalfilm coated on a solid substrate, or by chemically binding to a suitablereceptor that is covalently bound to a solid substrate (Figure 8.13). Adsorption,absorption, and binding occur at the interface between the solutioncontaining the analyte and the substrate’s surface, the thin film, or thereceptor. Although the amount of extracted analyte is too small to measureusing a conventional balance, it can be measured using a quartz crystalmicrobalance.The measurement of mass using a quartz crystal microbalancetakes advantage of the piezoelectric effect. 10 The application of an alternatingelectrical field across a quartz crystal induces an oscillatory vibrationalmotion in the crystal. Every quartz crystal vibrates at a characteristic resonantfrequency that depends on the crystal’s properties, including the massper unit area of any material coated on the crystal’s surface. The change inmass following adsorption, absorption, or binding of the analyte, therefore,can be determined by monitoring the change in the quartz crystal’s characteristicresonant frequency. The exact relationship between the change infrequency and mass is determined by a calibration curve.8D.2 Quantitative ApplicationsParticulate gravimetry is important in the environmental analysis of water,air, and soil samples. The analysis for suspended solids in water samples,for example, is accomplished by filtering an appropriate volume of a well-10 (a) Ward, M. D.; Buttry, D. A. Science 1990, 249, 1000–1007; (b) Grate, J. W.; Martin, S. J. ;White, R. M. Anal. Chem. 1993, 65, 940A–948A; (c) Grate, J. W.; Martin, S. J. ; White, R. M.Anal. Chem. 1993, 65, 987A–996A.