Ion selective electrodes utilizing a ferrocyanide doped redox active screen-printed solid contact - impact of electrode response to conditioning

Abstract

A novel sensing system was developed using a ferrocyanide-doped screen-printed carbon electrode as an ion-to-electron transducer in ion-selective electrodes (ISEs), which were further applied as a model system to investigate the possibility of a calibration-limited measurement approach for potassium. The novel sensing system offers high piece-to-piece standard potential reproducibility between K+-ISEs in the operational/plant fertilizer ion activity range of 10−1 to 10−4 M K+ (s.d. 0.7 to 3.6 mV, n = 3). Stable potential readings (± 2.8 mV) were found for electrodes conditioned in deoxygenated solutions (from 6 h to 27 h) and in solutions exposed to air (12 to 36 h). The importance of optimizing electrode conditioning to achieve stable limited-calibration measurements was indicated. The direction and magnitude of the potential drift of the ISEs were ultimately found to be dependent on the presence of O2 in the solution and hydration of the ISE. This reflects how the initial redox state of ISEs employing redox-active molecules could be perturbed by the environment. The new design of the ISEs was finally used to conduct a limited-calibration measurement of potassium in fertilizer solutions with a low drift (< 3 mV) at 24 h compared against an initial calibration conducted at 6 h.