The ionization source, as one of the most important parts of ion mobility spectrometry (IMS), greatly affects the performance of the instrument in analysis of chemical compounds, especially explosives. The radioactive 63Ni is the most common ionization source used in commercial IMS instruments. Despite the advantages of 63Ni, its use requires special permission. It is also expensive and its application is associated with radiation threats. In addition, the radioactive ion source cannot be used in the presence of corrosive gases as well as high-temperature condition. Alternative ion sources are usually the corona discharge and UV lamp with their own advantages. However, Corona discharge in air produces NOx that reduces the instrument sensitivity for some chemical compounds especially explosives. On the other hand, negative ions, cannot be directly obtained through photoionization with a UV lamp. In addition, the UV source has limited lifetime and low sensitivity. Therefore, the development of new ionization methods, especially in negative mode and in air, is necessary. The ion attachment to molecules in gas phase is very important, so that in many analytical techniques, alkali ions are used as an easy technique for ionization of biological molecules. Alkali ions are easily produced by thermal ionization of alkali salts. However, stability, lifetime and the ion current intensity are important. In the first part of this thesis, an alkali ion source based on alkali halide salts doped in nano-γ-alumina (Al2O3) was fabricated. The lifetime of the ion source for different alkali halides was measured to be in the range of 216 to 960 h. It consists of a fine Nichrome filament (diameter of 200m) coated with alkali salts impregnated with nano alumina as the thermal ionization source. Depending on the polarity, the ion source produces both alkali and halide ions. The total ion current emitted from the source for 11 mg of nano-particles loading on the filament was about 2A, that is comparable to the corona discharge. The application of the new ion source in ion mobility spectrometry was demonstrated by observing ion mobility spectra of organic compounds ionized via cation attachment reaction. In another part, a dopant-assisted thermal ionization source was introduced that works perfectly in air. A simple, cost-effective and stable Cl- ion source with high current was designed and constructed. It consists of a hot platinum filament (100 m in diameter) that CCl4, CHCl3, CH2Cl2, or C6H5Cl vapors as dopants were introduced in its vicinity. The ion source was eva‎luated by recording the ion mobility spectra of common explosives, including TNT, RDX, and PETN in the air. In the final parts, attempts were made to solve the two limitations in ion mobility spectrometry. The two are; 1- due to competition in ionization, some species prevent others from being ionized, and therefore simultaneous identification of two species with different ionization will be difficult. 2- Some ions have similar mobility and reach the detector at the same drift time (peak overlapping). The proposed solution is to separate the species in the ionization process, and then enter the drift region in an order. In fact, the ionization region acts as a separator, like GC, and the drift region identifies the ions. To demonstrate the application of this idea, a hot filament was used as a separator for alkali ions. Alkali elements with different ionization tendency left the surface based on their ionization energy and were detected in the drift tube.

محمود تبريزچي

حسين فرخ پور، كيومرث زرگوش

حسن قاضي عسكر، محمد ژياني، رضا اميديان