Novel surface acoustic wave-interdigitated array electrode gas sensor for dissolved ammonia

 A novel surface acoustic wave-interdigitated array electrode (SAW-IDA) ammonia gas sensor is proposed. A gas-permeable membrane is employed to separate the buffer solution in the inner cell of the gas-sensing probe from the sample solution in the detection cell. The response of the IDA conductive electrodes is based on the impedance change of the buffer solution during ammonia adsorption. Therefore, this gas sensor overcomes the influence of water vapour in the conventional film-coated SAW gas sensor and can be used for the detection of gases in aqueous solutions. The ammonia sensor exhibits a favourable frequency response to 5×10^-7–1×10^-3 mol/l ammonia. The optimal buffer composition and probe parameters have been determined. Dynamic range, response time, selectivity, and temperature drift are discussed. The ammonia sensor was also applied to the determination of serum ammonia. Results were in good agreement with those from the conventional enzymatic-spectrophotometric method. Received: 1 December 1995/Revised: 9 April 1996/Accepted: 14 April 1996