Non-invasive optical chemical sensor based on polyaniline films for detection of ammonia and acetic acid solutions

Polyanilines (PANI) are viable materials for use in optical chemical sensor. Thin films of PANI readily deposit on polystyrene sheets when aniline is chemically polymerised in hydrochloride acid solution. The films have been characterised by absorption spectra in visible region between 400-800 nm. They undergo pH-dependent changes in their absorption spectra in the physiological pH range. Based on this characteristics, they respond toward volatile analyte, i.e. ammonium and acetic acid solutions, have been investigated for their employment in non-invasive analysis. Here, the PANI films was employed for head space detection of ammonium and acetic acid solutions at 610 and 590 nm, respectively. The calibration curves were obtained over the concentration range at 0-0.16 M for ammonia and wider range (0-100%) for acetic acid solution respectively, with a detection limit (3σ) of 0.01 M for ammonia and 5% for acetic acid solution. With response time 20 min and 15 min for ammonia and acetic acid, respectively. The main advantage of these sensors is that no reagent indicator is needed because the PANI film itself acts as both matrix support and the indicator, compatible with solid state instrument, and easily be prepared.