Disposable optical tongue for alkaline ion analysis

A disposable optical tongue has been developed with a two-sensor array prepared on a transparent support. The array consists of polymeric membranes working by ionophore–chromoionophore chemistry with non-specific behaviour controlled by the crown ether-type ionophore present. The system was used for the simultaneous determination of Na(I) and K(I) ions in natural waters. The imaging of the element – after reaction for 3 min with the solution – by a conventional scanner makes it possible to calculate the hue coordinate H of the HSV colour space used as the analytical parameter. The signals were processed using an optimized multilayer Artificial Neural Network (ANN). The individual sensing membranes show good precision (0.3% RSD) and lifetime (around 45 days in darkness). The tongue works over a wide dynamic range (1.0 × 10−4 to 0.1 M both in Na(I) and K(I)) and when the procedure was applied, the Mean Square Error obtained by the ANN approach was 0.0064 for the prediction of K(I) and 0.0451 for Na(I). The procedure was used to analyze Na(I) and K(I) in different types of natural waters (tap and mineral), validating the results against a reference procedure.