Novel Enhancements and Analytical Applications of Amperometric Nitric Oxide (NO) Sensors

Abstract

Improvements to the selectivity of the Shibuki-design and solid-polymer electrolyte (SPE) based amperometric NO sensors are described in this dissertation. Novel applications of SPE-based NO sensors are also demonstrated with results compared with those obtained using chemiluminescence as a reference method. The selectivity with respect to aqueous-phase interfering species of Shibuki-type sensors is substantial; however, certain gas-phase species such as CO are major interferences. By increasing the pH of the internal electrolyte solution, the selectivity of Shibuki-design sensors vs. CO can be improved by up to 100-fold (Chapter 2). This improvement is the result of more extensive Pt-oxides formed on the electrode surface that inhibits CO adsorption. Gas-phase detection of NO requires a high surface area electrode, which can be deposited into the surface of a solid-polymer electrolyte (SPE) such as Nafion (Chapter 3). Pt-Nafion sensors exhibited excellent performance with a limit of detection (LOD) of 4.3 ± 1.1 ppb and response time under 5 s. Detection of NO released from NO-donor doped biomedical polymer films and electrochemically reduced nitrite solutions was performed using Pt-Nafion sensors and repeated using chemiluminescence. Strong agreement was found for both the NO-releasing films and the electrochemically reduced nitrite solution. In Chapter 4, several strategies were explored to enhance the selectivity of the Pt-Nafion sensors. Filtration of the sample gas was shown to be promising for the removal of CO (using an activated carbon fiber filter) and NH3 (using various acid traps) although further optimization of conditions is needed. Sampled current/sensitivity voltammetry of NO, CO and NH3 did not reveal a potential range with substantially improved selectivity and applying the principles developed in Chapter 2 (elevated internal electrolyte) also proved ineffective because Nafion cannot transport anions such as OH- or NO2-. Despite the current selectivity limitations, Pt-Nafion sensors have other useful applications (Chapter 5). The determination of nitrite and GSNO was examined with LOD of 26±5 nM and 17±10 nM, respectively. NO delivered by a cost-effective inhaled nitric oxide therapy (INO) system was monitored with no adverse effects from altering O2 concentration. NO2 sensing and scrubbing were also developed as potential safety measures.