Development of polymeric membrane-based hydrogen ion selective electrodes - A preliminary study

The potential responses of different polymeric membrane-based electrodes towards hydrogen ions were studied. Seven different membranes were used, each one of them differing from the others by the special additives incorporated in therm. The electrical resistivity measurement shows the ability of the special additives in considerably increasing the electrical conductivity of these membranes. The potential response towards hydrogen ions was found to be good for all the membranes, both in buffer solutions and in acid solutions. However, in acid solutions above pH 6.0, the deviation of the Nernstian slope from the theoretical value was very high. The deviation of the response potential from the theoretical value with the variation in the temperature of the medium was also studied. The results of such a measurement indicate that with the exception of a few, most of the membrane electrodes used in this study are not goad in this respect. The stability of these membrane electrodes was studied in buffer solutions for a period of about 25 hours. During the entire period of study there was no notable fluctuation in the response potential. The interference from alkali and alkaline earth metals for the hydrogen ion response was also studied and it was found that upto a concentration of 2.0 M mixed metal solution, there is no interference for the hydrogen ion response. Among the membrane electrodes used the one incorporating acetylene black as the special additive appears to be good because of its better electrical conductivity, better potential response, less deviation of the Nernstian slope from the theoretical value, better stability and the less deviation in the response potential with variation in the temperature of the medium.