en
Doctoral thesis
English

Development and Optimisation of Integrated Electrochemical Sensors for Aquatic Analysis

ContributorsForrest, Taraorcid
DirectorsBakker, Eric
Imprimatur date2023
Defense date2023
Abstract

Being able to precisely estimate the concentration of ions in a sample has always been of specific interest. Classical analytical techniques, such as titration or gravimetric analysis, were initially employed but showed limitations. Ion-selective electrodes (ISE) based on polymeric membranes were introduced a couple of decades ago and present a viable option to have a small, portable and affordable measuring platform for ions. They rely on potentiometry, an open-circuit measurement technique requiring low operating power, where a potential difference between the working and reference electrode of same cell is measured. The response of the working electrode as a function of ionic activity can be easily estimated using the Nernst equation. This thesis focuses on enhancing and improving the stability and longevity of potentiometric sensors. Chapter 1 will provide an overview of potentiometric sensors, focussing on the shift from liquid inner filling solution towards solid-contact ion-selective electrodes. Chapter 2 will present the use of thin membranes (nm thick) to speed up the development process of new ion-selective systems. To illustrate and showcase this new methodology, a hydrophobic transducing redox polymer, PEDOT-C14, was used for the first time as transducer in anion-selective membranes. Chapter 3 will focus more on the reference element in a potentiometric cell. The use of a regenerated cellulose-based dialysis membrane as liquid junction material was investigated. Liquid junction potential predictions according to the Henderson equation were made, but due to deviations from the theoretical behaviour, a new mathematical model was developed. This new simple calculation method, based on partial Donnan exclusion, showed good correlation with the rigorous Nernst-Poisson-Planck (NPP) simulation method. Chapter 4 presents the design and field testing of a potentiometric probe for nitrate analysis in freshwater. Sensors based on the previously developed PEDOT-C14 transducer were applied successfully in real conditions. To correct underlying drifts occurring on the electrode side, a one-point calibration step was implemented and pre-programmed to run at defined time intervals. A symmetrical reference element was also deployed for the first time on the field to reduce fluctuations caused by environmental factors. Chapter 5 presents the use of a self-plasticised matrix for ion-selective membranes. It is well known that the plasticiser that is added to the polymer to reduce its hardness tends to leach, causing drifts. In this work, using “Click” chemistry, a plasticiser-like moiety was grafted to azide-modified poly(vinyl chloride), inhibiting the leaching process. This newly developed polymer was successfully used in pH and potassium-selective electrodes. Chapter 6 investigates a new versatile transducing polymer, PEDOT-N3. This redox polymer is not naturally considered a good transducer due to its high hydrophilicity, but the azide groups offer a good platform to perform surface “Click” chemistry with hydrophobic groups. After surface grafting, the properties of these modified transducing layers were evaluated through contact angle measurements and then finally tested as ion-to-electron transducers ion solid-contact ion-selective electrodes. Chapter 7 offers a conclusion of the thesis while discussing possible outlooks and further development of this work.

eng
Keywords
  • Ion Sensing
  • Ion-Selective Electrodes
  • Potentiometric Sensor
  • Transducers
  • Aquatic Analysis
  • Click Chemistry
  • Electrochemical Sensors
Research group
Citation (ISO format)
FORREST, Tara. Development and Optimisation of Integrated Electrochemical Sensors for Aquatic Analysis. 2023. doi: 10.13097/archive-ouverte/unige:172738
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Thesis
accessLevelPrivateaccessLevelPublic 01/01/2025
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Technical informations

Creation11/07/2023 10:42:22 AM
First validation11/07/2023 3:28:41 PM
Update time11/07/2023 3:28:41 PM
Status update11/07/2023 3:28:41 PM
Last indexation05/06/2024 5:17:44 PM
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