This thesis describes the development and characterisation of two second-generation Fast Flowing Glow Discharge (FFGD) ion sources for analytical applications. These sources are interfaced with a quadrupole based mass spectrometer. Optimisation of the source parameters enables selective enhancement of the analyte ions whilst reducing the levels of the interfering ions (discharge gas and contaminant ions), producing a cleaner mass spectrum and higher analyte ion currents. Investigations have shown behaviour that is inconsistent with ionisation processes based solely on conventional models. This indicates that other ion-formation processes also occur within the argon glow discharge plasma, especially under short gas residence time conditions. Preliminary analytical work suggests that these sources achieve good internal precision (< 10%), detection limits in the 1-100 ppb range and Relative Sensitivity Factors in the range 0.4-5.0. These results indicate the potential of both sources for elemental analysis. The addition of 1-2% secondary hydrogen of the afterglow of the flowing plasma selectively enhances the metal ion signals. The interfering ions are also selectively reduced, to the point of negligible presence. These results are consistent with previous work from this laboratory, which suggests that the ions sampled from short residence time plasmas are as a result of neutral ionisation processes involving highly excited state species close to the ion exist aperture. Ionisation is caused by field/chemi-ionisation reactions at the ion exit aperture. The work in this thesis demonstrates that the Fast Flowing Glow Discharge source can be used as a sensitive elemental technique. In a separate piece of work, Collision Induced Dissociation Mass Spectrometry was used to investigate the pressure and temperature effects on the thermal (low energy) ionisation processes in cyclohexane. Although the project was unsuccessful in distinguishing the presence of the three C<sub>6</sub>H<sub>11</sub><sup>+</sup> isomers, the work is instructive with regards to the limitations of the technique used.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:636622 |
| Date | January 2002 |
| Creators | Williams, D. R. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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