A surface fit approach with a disposable optical tongue for alkaline ion analysis

• Published in: Analytica chimica acta 2011-05, Vol.694 (1), p.128-135
• Main Authors: Erenas, M.M., Piñeiro, O., Pegalajar, M.C., Cuellar, M.P., de Orbe-Payá, I., Capitán-Vallvey, L.F.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Answer surface modelling; Chemistry; Color; Darkness; Disposable optical tongue; Exact sciences and technology; Flatbed; General, instrumentation; HSV color space; Mathematical analysis; Mathematical models; Membranes; Sodium and potassium determination; Tongue; Water analysis
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2011.03.043

A disposable optical tongue for the alkaline ions Na(I) and K(I) is described. The two-sensor layout prepared on a transparent support consists of non-specific polymeric membranes working by ionophore–chromoionophore chemistry. The non-specific behavior of the membranes was controlled by means of the crown ether-type ionophore present. The imaging of the tongue, after reaction for 3 min with the unknown solution, by means of a conventional flatbed scanner working by transmission mode, makes it possible to calculate the H (hue) value of the hue, saturation, value (HSV) color space used as a robust and precise analytical parameter. The modelling of the response of the two-sensor tongue as a sigmoidal surface is used to characterize the behavior of the tongue and as a basis to infer the concentration values. To compute the concentration of two analytes from the two hue values obtained using the optical tongue, a surface fit approach was used. The tongue works over a wide dynamic range (1.0 × 10 −4–0.1 M both in Na(I) and K(I)). The sensing membranes show good intramembrane (1.4% RSD) and intermembrane precision (0.71% RSD) and lifetime (around 45 days in darkness). 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.