PH INDICATOR BASED AMMONIA GAS SENSOR - STUDIES OF SPECTRAL PERFORMANCE UNDER VARIABLE CONDITIONS OF TEMPERATURE AND HUMIDITY

Polymer-dye films, incorporating immobilized Bromocresol Purple pH indicator, can be used for ammonia gas sensing under the temperature and humidity variations that can occur during field operating conditions. To reveal the spectral features of the polymer-dye films, comparative spectral studies of the indicator dissolved in water and immobilized on the polymer matrix were performed. The modified absorption band of the immobilized indicator base form indicates the formation of an indicator-polymer ionic complex. Variations in the temperature (20-40-degrees-C) and relative humidity (50-85%) of the monitored ammonia gas produced noticeable distortions of the short-wavelength wing of the band profile and also of its peak. The long-wavelength wing of the band profile was relatively stable under these conditions and demonstrated a good correspondence to the Gaussian-shaped curve.