Detection of Amine Gases by Color Changes of Acid-Base Indicators Supported on Inorganic Films

Color-change behavior of acid-base indicators loaded on ceramic particles upon exposure to amine gases has been investigated so as to establish guidelines for fabricating optical amine gas sensors. Among several kinds of silica gel used as ceramic supports, the most excellent sensing property was achieved with the ceramic film consisting of spherical silica gel powder of 120 nm in diameter. It was revealed that existence of an adequate amount of adsorbed water on the silica gel was indispensable for the response to amine gases, and that sensitivity is then affected by relative humidity in atmosphere. It was also found that sensitivity tended to increase, and response time tended to shorten for an amine gas exhibiting a smaller pK_b value. The recovery time was not a function of the pK_b value, but shortened for an amine gas exhibiting higher vapor pressure