Development of an impedentiometric electronic tongue

A study aiming at the discrimination of basic tastes by measuring the variations of the electrical impedance of a sensor array is presented. In the last decade many kinds of partially selective sensors have been developed, both for gaseous and liquid compounds, to be used into arrays capable of generating characteristic fingerprints of complex samples. Relevant data are analysed by pattern recognition techniques, mimicking the functionality of the human sense of smell and taste. In the case of electronic tongues, three measurement techniques are mainly used for sample analysis, i.e. potentiometry, voltammetry and conductimetry. In this work, the electrical impedance of a sensor array was measured at a frequency of 150 Hz by means of an impedance meter. The measurement process was automated; a mechanical arm and a rotating platform controlled by a data acquisition card and a dedicated software allowed the sequential dipping of sensors in the test solutions. The array was composed of five sensors of three different types based on carbon nanotubes or carbon black dispersed in polymeric matrices and doped polythiophenes. Measurements were carried out on 15 different solutions representing the five basic tastes (sodium chloride, citric acid, glucose, glutamic acid and sodium dehydrocholate for salty, sour, sweet, umami and bitter respectively) at three concentration levels comprising the human perceptive range. More than one hundred measurements were carried out for each sample in a six month period to evaluate the system repeatability and robustness. A fairly good degree of discrimination was obtained analysing the data by linear and non linear pattern recognition techniques.