EVALUATION OF ACOUSTIC-EMISSION AS A MEANS OF QUANTITATIVE CHEMICAL-ANALYSIS

The viability of acoustic emission as a method of quantitative analysis was investigated and a sensor based on this principle is described. Acoustic transduction is achieved through the use of the enzyme catalase immobilized on the surface of an acoustic transducer. Catalase accelerates the conversion of dissolved hydrogen peroxide to oxygen and water and the oxygen effervescence is monitored acoustically. The limit of detection is determined by the rates of diffusion of peroxide to the surface and dissolved oxygen away from the surface. A limit of approximately 2 mM was consistently attained. Although this level may be useful for certain applications, it precludes the useful coupling of the catalase reaction with other peroxide producing reactions in most instances. Analytical alternatives based on the inhibition of catalase are discussed. The characteristics of the signals produced are described and the utility of various measurement modes (pulse counting, d.c. level, frequency) for calibration is considered. Counting of acoustic events was found to produce the best linear response. Good control of the bubble formation process is essential for measurement repeatability.