Remote optical detection of low concentrations of aqueous ammonia employing conductive polymers of polyaniline

Experimental results of the evaluation of the optical response of polyaniline films obtained by the chemical bath method when they are exposed to low concentrations of aqueous ammonia are reported. The optical transmittance of the polyaniline polymers was measured and analyzed in the wavelength interval of [350–1100 nm] to determine its optical sensitivity to different concentrations of ammonia. We have developed an optical sensor system based on the power ratio of transmittance for monitoring ammonia employing a polyaniline film, multimode optical fiber and a pigtailed laser diode at 975 nm. The variation of the power ratio was from 0.409 to 0.575 in the interval of [3–100 ppm] of ammonia. The slope of the calibration curve of the optical technique is 1.71 × 10−3/ppm. The polyaniline films employed as a sensing material for the optical detection of aqueous ammonia have a fast response time and a fast regeneration time of less than 10 sg at room temperature.