Novel autocalibration strategy for disposable potentiometric test strips

Potentiometry, particularly involving ion-selective electrodes (ISEs), is widely employed in laboratories due to its selectivity and compatibility with portable instruments. However, ISEs face a drawback —instability over time, requiring frequent calibration for precise and reliable results. This manual calibration process contradicts the user-friendly concept and inhibits the development of single-use quantitative devices for untrained personnel. To solve this limitation, a novel potentiometric autocalibration procedure, which is automated, is presented, and successfully tested for the first time with versatile potentiometric disposable test strips to perform the determination of chloride ion in sweat as a demonstrator. The test strips are based on a cyclic olefin copolymer platform, where two identical Ag/AgCl chloride ISEs are integrated, one acting as indicator and the other as reference electrode. Comparison of chloride results in real sweat samples between those obtained with the proposed test strips performing the novel autocalibration procedure and using ion chromatography reveals that the automated procedure effectively allows quantitative chloride ion analysis with good analytical features: linear range from 10 to 150 mM (covering the pathological range), average inter-method error of 7 % and average RSD between test strips of 4 %. By carefully selecting the initial solution composition in direct contact with each electrode, the autocalibration ensures that potentiometric test strips can be calibrated just before its use without requiring conscious user involvement. This breakthrough not only streamlines the process but also opens the possibility for the development of cheap disposable potentiometric test strips, accessible to non-experts operators, to quantitatively determine selected analytes in different fields.