New approaches to polyaniline optical sensors: pH, acetic acid and amonia determination

Optical sensors based on polyaniline (PAn) for pH, volatile acetic acid and ammonia determination are presented. The main advantage of these sensors i s that no indicator dye is needed because the polymer itself acts as both t he matrix support and the indicator. Although PAn has already been used for pH optical sensor, the sensitivity of the optical sensor to this parameter has been improved by using a different oxidant (iron(III) chloride). The a nalytical applications of the PAn films have also been extended to volatile compounds dissolved in aqueous solution (acetic acid and ammonia). To this end PAn films were covered with a thin silicone film (1.32 x 10(-4) g cm(- 2)), only permeable to gases, and therefore independent on the pH of the so lution. These films have been characterised for reversible acetic acid dete rmination and have a linear range from 0.02 to 0.6 M and an RSD of 1.9%. Th eir application to vinegar samples was in agreement with that obtained by t he Official Method of Analysis. The procedure was also used for ammonia det ermination (linear range from 1.8 x 10(-3) to 1.8 x 10(-4) M); the sensor, however, did not exhibit reversibility.