A CONDUCTIMETRIC SYSTEM BASED ON POLYANILINE FOR DETERMINATION OF AMMONIA IN FERTILIZERS

A simple conductimetric system to determine ammonia concentration usin g a sensor based on a conductor polymer was developed. The sensitive e lement to ammonia is a thin polyaniline film deposited by chemical syn thesis in an acrylic substrate prepared before hand with two graphite electrodes. The conductance of the polyaniline film decreases when exp osed to the ammonia gas and this variation can be related to the ammon ia concentration. To determine ammonia in fertilizer samples a system consisting of a measurement cell, a conductivity meter and a strip cha rt recorder was used. The results were compared with those obtained by three different laboratories employing a Kjeldahl method and are in g ood agreement. The detection range of the system was 0.6 to 3.7 mu g.m L(-1) with a response time of 4 minutes. The relative standard deviati on of the proposed method was about 5%.