MODELS AND METHODS OF DETERMINING THE TRANSIENT-RESPONSE OF ION SENSORS - COMPARISON WITH IMPEDANCE SPECTROSCOPY

This paper deals with the study of models and methods for determining the transient response function of ion sensors (ion-selective electrodes, ISEs), especially in our case sodium sensors. Theoretical models have been studied, such as the Rechnitz-Hameka model, the Toth and Pungor model and the Markovic-Osborn model. The methods studied are the dipping method, which involves two separate solutions for step generation, and the injection method, which involves a carrier solution with a small sample solution, These methods are compared with a fast system realized for this purpose. Recorded data are fitted to mathematical models and the response time is determined and compared to the relaxation time obtained by impedance spectroscopy with a 1250-Schlumberger analyser. Actually, the results obtained show a very fast response time of about 50 ms for sensors based on NASICON material, which is ten times faster than those of usual sensors (Solea-Tacussel).