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Title: Thin-film optical sensors for carbon dioxide
Author: Wild, L. B.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1999
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In Chapter 3 a homologous family of dialkyl phthalates is used to investigate the effect of plasticiser/polymer compatibility on the response characteristics of transparent, thin-film optical gas sensors for carbon dioxide. A strong correlation is found between plasticiser/polymer compatibility and sensitivity in phenol red/ethyl cellulose CO2-sensitive films. This relationship applies to CO2-sensitive films based on other polymers such as polystyrene and poly(methyl methacrylate). This relationship also extends to optical O2-sensitive films, implying that the relationship is general for thin film optical sensors. In Chapter 4 an optical sensor is developed for breath-by-breath gaseous carbon dioxide analysis. The detector is based on a general formulation described in previous work where a phase transfer agent, tetraoctylammonium hydroxide (TOAOH), is used to incorporate a hydrophilic pH-sensitive dye into a hydrophobic plastic film to create an effectively solid-state colourimetric sensor. In this work the formulation has been modified to yield a sensor which is capable of responding to clinically important levels of carbon dioxide (0.1-5%) in less than 200ms. This is comparable with the response of commercially available capnometers based on infrared sensing of carbon dioxide, which are currently widely used for clinical analysis. In Chapter 5 the hydrophobic bases, tetraoctylammonium hydroxide (TOAOH), tetrakisdecylammonium hydroxide (TKAOH) and tetradodecylammonium hydroxide (TDAOH), are used to solubilise the anionic form of m-cresol purple in ethyl cellulose to create colourimetric thin-film sensors for monitoring carbon dioxide in the gas phase and dissolved in solution. When used for making dissolved carbon dioxide measurements both TKAOH and TDAOH appear significantly more resistant toward interference by protons or other ions at high concentration when compared to TOAOH, the hydrophobic base which has been used for such work in previous studies. In Chapter 6 the preparation and characterisation of three different plastic thin-film colourimetric sensors for gaseous ammonia are described. Each of these film optrodes gives a reproducible and reversible response towards gaseous ammonia. The sensitivity of the film sensors was found to be dependent upon the pKa of the encapsulated dye. The sensitivity of the plastic film sensor decreases markedly with increasing operation temperature and the 90% response and recovery times are slow and activation-controlled.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available