Use of Rapid Reduced Electric Field Switching to Enhance Compound Specificity for Proton Transfer Reaction-Mass Spectrometry.
The high sensitivity of proton transfer reaction-mass spectrometry (PTR-MS) makes it a suitable analytical tool for detecting trace compounds. Its specificity is primarily determined by the accuracy of identifying the m/ z of the product ions specific to a particular compound. However, specificity can be enhanced by changing the product ions (concentrations and types) through modifying the reduced electric field. For current PTR-MS systems, this is not possible for trace compounds that would only be present in the reaction chamber of a PTR-MS for a short time (seconds). For such circumstances, it is necessary to change the reduce electric field swiftly if specificity enhancements are to be achieved. In this paper we demonstrate such a novel approach, which permits any compound that may only be present in the drift tube for seconds to be thoroughly investigated. Specifically, we have developed hardware and software which permits the reaction region's voltages to be rapidly switched at a frequency of 0.1-5 Hz. We show how this technique can be used to provide a higher confidence in the identification of compounds than is possible by keeping to one reduced electric field value through illustrating the detection of explosives. Although demonstrated for homeland security applications, this new technique has applications in other analytical areas and disciplines where rapid changes in a compound's concentration can occur, for example, in the Earth's atmosphere, plant emissions and in breath. Importantly, this adaptation provides a method for improved selectivity without expensive instrumental changes or the need for high mass resolution instruments.
Development and applications of proton transfer reaction-mass spectrometry for homeland security : trace detection of explosives
This thesis investigates the challenging task of sensitive and selective trace detection of explosive compounds by means of proton transfer reaction mass spectrometry (PTR-MS). In order to address this, new analytical strategies and hardware improvements, leading to new methodologies and analytical tools, have been developed and tested. These are, in order of the Chapters presented in this Thesis, the switching of reagent ions, the implementation of a novel thermal desorption unit, and the use of an ion funnel drift tube or fast reduced electric field switching to modify the ion chemistry. In addition to these, a more fundamental study has been undertaken to investigate the reactions of picric acid with a number of different reagent ions. The novel approaches described in this thesis have improved the PTR-MS technique by making it more versatile in terms of its analytical performance, namely providing assignment of chemical compounds with high confidence. These techniques are going to be employed in the new generation of PTR-MS instruments being developed by KORE Technology Ltd. Although demonstrated for Homeland Security in this thesis, the developments made can be utilised for improved selectivity in areas such as atmospheric chemistry, and in the environmental, food and health sciences.
Thermodynamics on the Carbochlorination of Titanium-bearing Ores
The equilibrium compositions of the multi-component, multi-phase and multi-reaction system of carbochlorination of titanium-bearing ores are calculated with HSC, a computational chemistry software. The thermodynamic equilibrium calculation of the reaction system shows that a complete conversion of titanium-bearing ores is feasible at a temperature near 200oC. At temperatures ranging from 800 to 1600oC, the products of the reaction system are all in gaseous phase. Thermodynamic analysis accords with the industrial practice. The simulated results provide reasonable scientific basis for improving suitable technological conditions of the carbochlorination reduction.