Traditionally, the condition of hydroponic nutrient solutions used in controlled environment or greenhouse plant production is obtained by monitoring solution pH and electrical conductivity. These parameters provide greenhouse operators with an overall sense of the solution quality, but do not provide information on individual components of the fertilizer solution. Considering that plant nutrient uptake requirements vary with crop, growth phase and environment, real-time ion-selective measurements represent a significant technological advance in the management of recirculating nutrient solutions. The capacity for the monitoring and control of individual ions in the nutrient solution is the last remaining environment variable for which reliable feedback control does not exist in controlled environment plant production. This technology development study focussed on optical ion-selective sensors, termed ‘optrodes’, for potassium and calcium sensing within nutrient solution. Bulk optrode absorption-based sensors, tailored explicitly for nutrient ion activities within typical hydroponic solutions were theoretically modelled, fabricated and experimentally tested. Experimental data on sensor response time, measuring range, selectivity, repeatability, lifetime and influence of temperature were compiled. These ion-selective bulk optrode membranes were integrated into a custom instrument combining a light source, mini-spectrometer, optical fibres and other associated components. Monitoring and control software was written that collected and converted optical measurements into estimated nutrient ion activities for use in managing nutrient solution quality. Implemented spectral averaging, normalization and ratiometric computations and techniques resulted in sensors that offered the advantage of auto-calibration. The sensors met selectivity requirements in half strength Hoagland nutrient solution and provided repeatable measurements in solutions of different ion activity levels. Potassium and calcium selective membranes demonstrated lifetimes of 30 to 50 hours when constantly immersed in nutrient solution. Strategies for their operational implementation in plant growth systems based upon experimental testing are proposed as are suggestions for future study. The low mass, low volume, low cost and robust nature of these optrodes offer a promising technology for future space-based plant production systems and give them excellent terrestrial technology transfer potential.

This dissertation presents chemical sensors that are based on an emerging optical fiber sensing technology for the determination of the presence and concentration of hydrogen peroxide (H2O2) at low concentrations. The motivation to determine hydrogen peroxide lies on the fact that this chemical species is generated as a by-product of the operation of hydrogen-based polymer electrolyte membrane fuel cells (PEMFCs), and the presence and formation of this peroxide has been associated with the chemical degradation that results in low durability of PEMFCs. Currently, there are no techniques that allow the hydrogen peroxide to be determined in situ in PEMFCs in a reliable manner, since the only report of this type of measurement was performed using electrochemical techniques, which can be affected by the environmental conditions and that can alter the proper operation of the PEMFCs. The sensors presented in this dissertation are designed to detect the presence and quantify hydrogen peroxide in solution at the conditions at which PEMFCs operate. Since they are made using fused silica optical fibers and are based on a spectroscopic technique to perform the detection of H2O2 , they are not affected by the electromagnetic fields or the harsh chemical environment inside PEMFCs. In addition, they are able to still detect the presence of H2O2 at the operating temperatures. The construction of the sensing film on the tip of an optical fiber and its small size (125 µm diameter), make the sensors here developed an ideal solution for being deployed in situ in PEMFCs, ensuring that they would be minimally invasive and that the operation of the fuel cell would not be compromised by the presence of the sensor. The sensors developed in this dissertation not only present design characteristics that are applicable to PEMFCs, they are also suitable for applications in other fields such as environmental, defense, and biological processes. / Graduate / 0548 / 0756 / 0791 / jfbotero@gmail.com

This dissertation presents chemical sensors that are based on an emerging optical fiber sensing technology for the determination of the presence and concentration of hydrogen peroxide (H2O2) at low concentrations. The motivation to determine hydrogen peroxide lies on the fact that this chemical species is generated as a by-product of the operation of hydrogen-based polymer electrolyte membrane fuel cells (PEMFCs), and the presence and formation of this peroxide has been associated with the chemical degradation that results in low durability of PEMFCs. Currently, there are no techniques that allow the hydrogen peroxide to be determined in situ in PEMFCs in a reliable manner, since the only report of this type of measurement was performed using electrochemical techniques, which can be affected by the environmental conditions and that can alter the proper operation of the PEMFCs. The sensors presented in this dissertation are designed to detect the presence and quantify hydrogen peroxide in solution at the conditions at which PEMFCs operate. Since they are made using fused silica optical fibers and are based on a spectroscopic technique to perform the detection of H2O2 , they are not affected by the electromagnetic fields or the harsh chemical environment inside PEMFCs. In addition, they are able to still detect the presence of H2O2 at the operating temperatures. The construction of the sensing film on the tip of an optical fiber and its small size (125 µm diameter), make the sensors here developed an ideal solution for being deployed in situ in PEMFCs, ensuring that they would be minimally invasive and that the operation of the fuel cell would not be compromised by the presence of the sensor. The sensors developed in this dissertation not only present design characteristics that are applicable to PEMFCs, they are also suitable for applications in other fields such as environmental, defense, and biological processes. / Graduate / 0548 / 0756 / 0791 / jfbotero@gmail.com

Hydrogen peroxide (H2O2) is extensively used in a broad range of industrial and medical applications, such as aseptic processing of food and pharmaceuticals, disinfection, water treatment plants, and decontamination of industrial effluents. H2O2 is believed to be responsible for chemical degradation of polymer membranes in Polymer-Electrolyte-Membrane (PEM) fuel cells. Therefore, a versatile H2O2 sensor that functions in different environments with different conditions is of practical importance in various fields. This dissertation presents the fabrication of a fiber-optic H2O2 sensing probe (optrode) and its H2O2 sensing behavior in different conditions. An H2O2 optrode is fabricated using chemical deposition of Prussian blue (PB) onto the tip of a multimode optical fiber. Sensing tests are performed in aqueous solutions at a constant pH and different concentrations of H2O2. Sensing features of the optrode (i.e. repeatability, durability, and reproducibility) are assessed by performing multiple sensing tests with several optrodes. The results show the prepared optrode is able to detect concentrations of H2O2 in aqueous solutions at a constant pH of 4 and the optrode features a repeatable and durable response at this condition. The functionality of optrodes at different pH values is further investigated by performing additional sensing experiments. These experiments are carried out in aqueous solutions with different concentrations of H2O2 at different pH values (i.e. pH 2-7). The sensor detects the presence of H2O2 at a range of pH values. Sensing behavior of optrodes toward detection and measurement of H2O2 concentrations is studied at the pH value corresponding to an operating PEM fuel cell (i.e. pH 2). The optrode is able to detect concentrations of H2O2 at this condition with a repeatable and durable response. The stability of PB films, prepared through different conditions, is investigated to address the stability of optrodes at elevated temperatures. PB films are first deposited onto the glass slides through three different chemical processes, and then at different synthesis temperatures. The PB films are left in Phosphate-Buffer-Solutions (PBS) with pH 2 and at elevated temperatures for a day. Finally, PB films are characterized using Fourier transform infrared spectroscopy (FTIR) to analyze their stability following PBS processing at operating temperatures and pH value corresponding to an operating PEM fuel cell (i.e. 80 °C and pH 2). The results of these experiments illustrate the PB films prepared through the single-source precursor (SSP) technique and at synthesis temperatures above 60 °C remain stable after the PBS processing. The proposed optrode shows reliable sensing behavior toward detection and measurement of H2O2 concentrations in aqueous solutions at different conditions. The prepared optrode has the potential for being developed and used in different industrial and medical fields, as well as an operating PEM fuel cell, to detect and measure H2O2 concentrations. / Graduate / 0794 / 0548 / 0485 / hakbarik@uvic.ca

Se han desarrollado métodos basados en análisis por inyección en flujo multijeringa (MSFIA) para determinar automáticamente sulfuro en muestras ambientales y aguas residuales, con detección espectrofotométrica previa transformación química del analito (acoplamiento oxidativo del sulfuro con N-N-dimetil-p-fenilendiamina en presencia de Fe(III) para formar azul de metileno).- Sistema MSFIA con difusión gaseosa para aislar el analito de matrices complejas sin ningún pretratamiento manual de la muestra.- Sistema MSFIA con pre-concentración en fase sólida (optrodo de reflectancia difusa sobre disco de membrana) para determinar niveles traza. - Método MSFIA que combina separación y pre-concentración en línea del sulfuro, para ofrecer elevadas selectividad y sensibilidad.- Sistema MSFIA inteligente totalmente automatizado para determinar sulfuro en un amplio rango de concentraciones, capaz de auto-ajustarse sin ninguna intervención del analista.- Estudio comparativo de metodologías en flujo para determinar sulfuro en matrices acuosas. Se discuten críticamente distintas técnicas y sistemas de detección empleados. / Multisyringe flow injection analysis (MSFIA) systems for automatic determination of sulfide in environmental and wastewater samples have been developed exploiting spectrophotometric detection prior derivatization of the analyte (oxidative coupling of sulfide with N-N-dimethyl-p-phenylenediamine in presence of Fe(III) to form methylene blue).- A MSFIA system was coupled to gas-diffusion separation to achieve the isolation from complex matrices without any pre-treatment batch sample.- An optrode using disk-based solid-phase extraction in a MSFIA set-up is proposed to determine trace levels.- A hyphenated method that combines the separation and pre-concentration is presented reaching high selectivity and sensitivity. - A fully automated smart MSFIA system for sulfide monitoring in a wide concentration range is proposed choosing by itself the best approach to quantify the analyte without the analyst intervention.- A review of flow-based methodologies for sulfide determination in aqueous matrices is presented. The characteristics of automated protocols using several detection systems are discussed.

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