THEORY OF THE SURFACE-ACOUSTIC-WAVE IMPEDANCE SENSOR SYSTEM AND ITS APPLICATION TO THE END-POINT DETERMINATION IN TITRIMETRY

Theory and characteristics of the surface acoustic wave (SAW)/impedanc e sensor system in electrolyte solution are reported. This kind of sen sor was constructed by a 62-MHz SAW resonator and a pair of conductive electrodes in series. By using the circuit network analysis theory, t wo oscillation equations were derived and used to explain the frequenc y-shift response to solution conductance. Results showed that the sens or possesses high sensitivity to the solution conductivity and can be applied to conductivity measurements in solution. Its sensitivity and accuracy could be improved in the presence of a large amount of unreac ting foreign electrolytes. The sensor was successfully applied to four types of titration (acid-base, precipitation, oxidation-reduction and compleximetric titration) by monitoring the frequency-shift response. Factors influencing the frequencimetric titration curve were also inv estigated. Analytes at levels down to 1 X 10(-5) M could be determined by the proposed titration technique. The total acidity in several foo d samples was determined and the results were consistent with those ob tained by conventional methods.