This thesis discusses diverse electrochemical strategies for the determination of the concentration of the gases hydrogen sulfide, ammonia and halothane. The chemical tagging of sulfide by a variety of structurally diverse substituted benzoquinone species was studied over a wide range of pH (2<pH<10). Each derivative was found to respond to increasing concentration of sulfide (typically over a range 10-200 μM). The electrochemically initiated reaction of N,N-diethyl-pphenylenediamine (DEPD) with sulfide in N,N-dimethylformamide (DMF) was next examined with quantitative detection of sulfide (linear range= 28-3290 μM, LoD= 22 μM) achieved by analysis of the increase in the second oxidation wave. This is consistent with the sulfide attacking the doubly oxidised species in a 1,4-Michael addition. The direct oxidation of sulfide at a nickel hydroxide film on a nickel electrode in alkaline solution has provided the basis for the design of a simple and inexpensive sensor for monitoring H<sub>2</sub>S in the range 20-200 μM. More sensitive (LoD= 1 (μM) amperometric detection of sulfide was obtained at modified nickel electrodes in acidic media in which sulfide was stripped from the nickel oxide layer. This approach was exploited further by using nickel modified screen printed carbon (Ni-SPC) electrodes as economical and disposable sensors for sulfide. Next, two different strategies for determining gaseous ammonia in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluromethylsulfonyl)imide, [EMIM][N(Tf)<sub>2</sub>], and in DMF are described. The first approach exploits the effect of ammonia as a proton acceptor species on the anodic oxidation of hydroquinone, resulting in a linear detection range from 10 to 95 ppm ammonia (LoD= 4.2 ppm). The second approach is based on the direct oxidation of ammonia in either DMF or [EMIM][N(Tf)<sub>2</sub>]. The possibility of photochemically induced electrocatalytic processes within microdroplets containing p-chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone, TCBQ) was examined as a means of detecting the anaesthetic gas halothane.</p> Finally, two of the more promising routes for sulfide detection were studied at elevated temperatures (up to 70 °C) with a view to developing H<sub>2</sub>S sensors capable of meeting the demands of oilfield applications.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:409033 |
| Date | January 2004 |
| Creators | Giovanelli, Debora |
| Contributors | Compton, R. G. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:fd447153-b6dd-4be1-aae5-4ece5dc36856 |
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