Talanta Talanta 43 (I 996) I25- I34 A polypyrrole-based amperometric ammonia sensor * Ilkka Lghdesmgki, Andrzej Lewenstam, Ari Ivaska* Laboratory qf Analytic,al Chrmistr~~, Aho Akadrmi University, FIN-20500 Turku-kbo, Finland Received 4 April 1995: accepted 31 July 1995 Abstract An ammonia sensor is described in this work. The sensing membrane is a thin layer of oxidized polypyrrole (PPy) on a platinum substrate. This sensor is used as the working electrode in a conventional three-electrode system for amperometric measurement of ammonia in aqueous solutions in the potential range of + 0.2 to + 0.4 V (vs. Ag/AgCl). Contact with ammonia causes a current to flow through the electrode. This current is proportional to the concentration of free ammonia in the solution and ammonium ions do not contribute to the measured signal. The signal is due to reduction of PPy by ammonia with subsequent oxidation of PPy by the external voltage source. The sensor is able to detect ammonia reproducibly at the ,DM level. The main interference is the doping effect of small anions such as Cl - and NO,, also giving a response on PPy at the mM level. This anionic response can, to a certain degree. be reduced by covering the polymer surface with dodecyl sulfate. The sensor gradually loses its activity when exposed to ammonia concentrations greater than 1 mM. The sensor has been tested by the flow injection analysis technique. Kqmwcis: Ammonia sensor: Polypyrrole; Conductive polymer; Amperometry: Flow injection analysis 1. Introduction Gaseous ammonia is known to reduce the oxi- dized form of the conducting polymer polypyrrole (PPy) [I]. Josowicz and Janata [2] utilized this property to prepare a sensor for gaseousammo- nia where oxidized PPy formed the active mem- brane. They used the conductivity of PPy as a measure of the concentration of ammonia in gaseoussamples. Trojanowicz et al. [3] described an amperomet- ‘Presented in part at the ESEAC ‘94 conference in Venice, Italy. May 1994. *Corresponding author. ric ammonia sensor for the determination of dis- solved ammonia in aqueous samples, where PPy deposited on platinum is the working electrode in a three-electrode system. They also presented the optimized conditions for preparation of the sensor and for measurement of ammonia. The influence of some common interfering species in clinical samples on the response of the sensor was also studied. The sensor was found to be deactivated in the processof detecting ammonia. In this work, we have further studied and tried to eliminate the interfering effect of common inorganic anions and cations. Sensor preparation and ammonia mea- surements were carried out under optimized con- ditions, as given in Ref. [3]. 0039-9140/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 0039.9140(95)01713-5