Abstract The simultaneous determination of NH 4 + and K + in solution has been attempted using a potentiometric sensor array and multivariate calibration. The sensors used are rather non-specific and of all-solid-state type, employ- ing polymeric (PVC) membranes. The subsequent data processing is based on the use of a multilayer artificial neural network (ANN). This approach is given the name “electronic tongue” because it mimics the sense of taste in animals. The sensors incorporate, as recognition elements, neutral carriers belonging to the family of the ionophoric antibiotics. In this work the ANN type is optimized by study- ing its topology, the training algorithm, and the transfer functions. Also, different pretreatments of the starting data are evaluated. The chosen ANN is formed by 8 input neurons, 20 neurons in the hidden layer and 2 neurons in the output layer. The transfer function selected for the hid- den layer was sigmoidal and linear for the output layer. It is also recommended to scale the starting data before training. A correct fit for the test data set is obtained when it is trained with the Bayesian regularization algorithm. The viability for the determination of ammonium and potas- sium ions in synthetic samples was evaluated; cumulative prediction errors of approximately 1% (relative values) were obtained. These results were comparable with those ob- tained with a generalized regression ANN as a reference algorithm. In a final application, results close to the ex- pected values were obtained for the two considered ions, with concentrations between 0 and 40 mmol L –1 . Keywords Sensor array · PVC membrane · Ion-selective electrode · Artificial neural networks · Ammonium · Potassium Introduction There is a recent trend, derived from the search for spe- cific, single analyte sensors, to use sensor systems. This is due to the existence of few almost perfect sensors which do not suffer from interferences, calibration drifts, noise effects or irreproducibilities. A first strategy was the use of automated analytical systems to adapt or solve some of these non-idealities. Certain introduced stages, such as sample conditioning, frequent recalibration, sample clean up or preconcentration, enhanced analytical performance but with higher cost and complexity. The more novel scheme is the use of multielement sensor arrays, which can use sensing devices with less restrictive characteristics. With this approach, the solution of situations or problems hard to cope with more classical alternatives, such as the clas- sification of foods and beverages, can be attempted. The use of a set of sensors instead of a single, perfectly selective sensor brings added advantages. Instead of ob- taining only a single data point, sensor arrays provide mul- tiple data points per sample, following the trend of obtain- ing information with higher dimensionality. This richer con- tent can provide additional chemical information, which in turn is used to differentiate multiple analytes and to dis- criminate interfering species. Information content can some- times be further enhanced using modulation schemes, ob- taining the so-called higher order sensor systems. The transducing approaches for sensor arrays cover al- most all the different sensing principles. Among others, there have been described arrays of mass sensors, chemo- resistors, optodes, voltammetric or potentiometric sen- sors. When the array is used to detect gaseous species, it is given the name “electronic nose” [1]. When it is used for liquid samples, the term “electronic tongue” starts to be used [2]. Both terms have been proposed in reference to animal senses. This is because these strategies share the general principle of having only few classes of differenti- ated receptors but, with cross term responses and overlap- ping selectivities, they discriminate against a multitude of species [3]. J. Gallardo · S. Alegret · R. Muñoz · M. De-Román · L. Leija · P. R. Hernández · M. del Valle An electronic tongue using potentiometric all-solid-state PVC-membrane sensors for the simultaneous quantification of ammonium and potassium ions in water Anal Bioanal Chem (2003) 377 : 248–256 DOI 10.1007/s00216-003-2042-7 Received: 22 January 2003 / Revised: 14 March 2003 / Accepted: 7 May 2003 / Published online: 19 July 2003 SPECIAL ISSUE PAPER J. Gallardo · S. Alegret · M. del Valle (✉) Sensors and Biosensors Group, Department of Chemistry, Autonomous University of Barcelona, Edifici Cn, 08193 Bellaterra, Catalonia, Spain e-mail: mdelvalle@gsb.uab.es R. Muñoz · M. De-Román · L. Leija · P. R. Hernández Bioelectronics Section, Department of Electrical Engineering, CINVESTAV, México DF, Mexico © Springer-Verlag 2003