The influence of PVC/KCl membrane fabrication on the potential stability of a solid-state Ag/AgCl reference electrode

• Main Authors: Yi-Min Wu, 吳伊敏
• Other Authors: 陳林祈
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/6npd7c

碩士 === 國立臺灣大學 === 生物產業機電工程學研究所 === 106 === Electrochemical sensor is widely applied in medical examination, agriculture and environmental monitoring. The major components of the sensor include working electrode and solid-state reference electrode (SSRE). While the reaction of interest is occurring on the working electrode, SSRE provides a basis to measure the potential of working electrode. By providing reference potential, SSRE has to reach its stable state first, and on current SSRE it takes more than 5 minutes, which is much longer than user requirement, i.e. within minutes. Thus, in this study, we develop a layered SSRE that can reach its stable potential in a timely manner, and ultimately enhance the accuracy of the sensor. The layered structures of SSRE from bottom to top include polyethylene terephthalate (PET) substrate, Ag/AgCl screen-printed electrode (SPE) layer, potassium chloride-polyvinyl chloride (KCl-PVC) layer and PVC layer. In previous studies, increasing the thickness and compactness of AgCl facilitates stabling the potential and extends the life of SSRE. Thus, in this study the Ag/AgCl SPEs is chlorized by immersing in FeCl3 solution to increase the deposition of AgCl on the surface of electrode. The results show that the chlorized electrode is less vulnerable to polarization, and the potential drift in 60 seconds is decreased to 1 mV. Furthermore, KCl-PVC layer is covered on the chlorized SPEs. The coverage and thickness of KCl are calculated to ensure that sufficient Cl- maintains reversible redox reaction with AgCl on the surface of SPEs. However, it is found that KCl dissolves into the analyte during measurement, which leads to the potential drifts especially in analyte of low concentration. Hence, an optimized PVC layer is covered on top of KCl to prevent KCl from dissolving. Secondly, different concentrations and thickness of PVC layers are covered on KCl-PVC layer. The results show that the ion diffusion on PVC layer may alter the liquid-junction potential, which is critical on potential drift and reproducible potential in different analytes. By implementing these approaches, the potential drift in 30 seconds of the optimized SSRE is decreased to 0.5 mV, and the response time is shortened to 25 seconds, which is significant improvement compared to the current SSRE. Finally, the optimized SSRE is used in cyclic voltammetry and applied with potassium ion-selective electrodes, and proved to be feasible in electrochemical sensing.