Investigation of dye-doped sol–gels for ammonia gas sensing

Sol–gel films doped with fluorescein (FL) and phenol red (PR) dyes were evaluated for their responses to ammonia gas. In a steady state, the sensors respond to the gas-phase ammonia evolved from ammonium hydroxide solutions in the range of 5 × 10−6 to 0.05 M for FL-doped gels, and 10−4 to 1 M for PR-doped gels. The sensors have high selectivity for ammonia against larger amines and moderate selectivity against methyl and ethylamines. The FL-gel exhibits rapid and reproducible response to dry NH3 gas samples of 9–50 ppm, while PR-gel is insensitive to ammonia in this low concentration range. The life-times of the sensors are over a year.