REPORT and Wohltjen's cyclopentadiene sensor (29) and Zellers's styrene and vinyl ace tate sensors (5,30), which are of partic ular interest because reagent is sus pended in a semiselective polymer film. Corrections are made for nonspecific sorption into the film by coating one side of a dual device with the reagentpolymer mixture and the reference side with the polymer alone. An additional advantage of these sensors is that re agents can be regenerated, whereas the cyclopentadiene-poly(ethylene maleate) system is generally irreversible. This approach has the advantage of in creased chemical specificity and can be useful when a well-known hazard exists or when the ambient environment is under partial control, such as in indus trial hygiene applications or in the monitoring of industrial processes. Future directions To date, no chemical vapor sensors have been developed that take advan tage of the sensitivity of the SAW de vice to changes in the shear elastic modulus of the coating material. Re cent investigations, however, have shown that the SAW device has poten tial for use in the characterization of polymeric materials. Parameters that
can be determined include the glass transition temperature (Tg), the melt ing temperature of crystalline poly mers (T m ), thermal expansion coeffi cients, and thermal relaxation activa tion energies (5). The SAW device pro vides a rapid, sensitive, and inexpensive alternative to existing methods. Future research will likely follow several paths. New SAW device config urations (e.g., resonators) and packag ing approaches offer potential for re ducing noise and drift. Different types of acoustic waves can be developed for chemical sensing in both liquid and va por phases. Continued vapor/coating interaction research should yield new coating formulations that will expand the range of analytes accessible to SAW device technology. Further development of pattern rec ognition algorithms should also strengthen the power of array sensors. Attempts are being made to use mod ern silicon micromachining techniques to facilitate total system miniaturiza tion of valves and pneumatic hardware often used to support the SAW sensor "chip." The successes of these efforts should make chemical sensing with SAW devices a method of choice for chemical analysis in the future.
References (1) Janata, J.; Bezegh, A. Anal. Chem. 1988,60,62 R. (2) Aucouturier, J. L.; Cauhape, J. S.; Destriaue, M.; Hagenmulle, P.; Lucat, C; Menil, F.; Portier, J.; Salardenne, J., Eds.; Proceedings of the International Meet ing on Chemical Sensors, July 1987, Bor deaux, France. (3) Transducers '87, Proceedings of the International Conference on Solid-State Sensors and Actuators-Transducers; To kyo, June 1987. (4) Proceedings of the IEEE Ultrasonic Symposium; Chicago, IL, October 1988. (5) Murray, R. W.; Heineman, W. R.; Jan ata, J.; Seitz, W. R. ACS Symposium Se ries, in press. (6) White, R. M.; Volltmer, F. W. Appl. Phys. Lett. 1965, 7, 314. (7) Brace, J. G.; Sanfelippo, T. S.; Joshi, S. G. Sens. Actuators 1988,14, 47. (8) Martin, S. J.; Ricco, A. J.; Ginley, D. S.; Zipperian, T. E. IEEE Trans. 1987, UFFC-34(2), 143. (9) Ballantine, D. S., Jr.; Rose, S. L.; Grate, J. W.; Wohltjen, H. Anal. Chem. 1986,58,3058. (10) Grate, J. W.; Snow, Α.; Ballantine, D. S., Jr.; Wohltjen, H.; Abraham, M. H.; McGill, Α.; Sasson, P. Anal. Chem. 1988, 60, 869. (11) King, W. H., Jr. Anal. Chem. 1964, 36(9), 1735. (12) Edmonds, T. E.; West, T. S. Anal. Chim. Acta 1980,117,147. (13) Wohltjen, H. Sens. Actuators 1984, 5, 307. (14) Wohltjen, H. Transducers '87, Pro-
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