STUDY OF DETECTION OF INORGANIC IONS BY ELECTROSPRAY MASS SPECTROMETRY AND DEVELOPMENT OF ION MOBILITY SPECTROMETRY AND ITS APPLICATIONS

This thesis focuses on the development of a novel drift tube and novel pulse circuit design for ion mobility spectrometry in combination with different ionization methods for various applications, as well as aspect of electrospray mass spectrometry of inorganic ions. The first project was the study of the measurement of a mixture of inorganic cations using an electrospray ion-trap mass-spectrometry normally used for neutral organic compounds. The mass spectra showed the production of solvent clusters, which could be minimized by making use of the collision-induced dissociation capability of the instrument as well as by heating of the inlet tube. The collision-induced dissociation (CID) voltages were optimized to reduce adduct and cluster formation. The use of an internal standard for construction of linear calibration lines was studied. The work showed potential for quantitation of mixtures of inorganic ions using the electrospray mass spectrometer. In the second project, a gas sensor based on a field asymmetric ion mobility spectrometer was constructed in-house, coupled with a Krypton lamp as ionization source. A rectangular pulse was employed as the separation waveform for the drift tube instead of the commonly used but less efficient bi-sinusoidal waveform. The device was used for qualitative and quantitative measurement of ethylene gas that is emitted by climacteric fruit. For selectivity in the detection of ethylene, a Krypton lamp with a specific radiation energy (eV) was employed, leading to high ionization efficiency of ethylene and with other compounds having higher ionization energies not being ionized. The device was applied to the determination of ethylene given off by 6 types of climacteric fruits, namely apples, bananas, kiwi fruit, nectarines, pears and plums. In the third project, the novel use of flexible printed circuit board material for the construction of drift tubes for ion mobility spectrometry was developed. The circuit board was etched out to give narrow copper stripes which when rolled up produced a tube with a series of circular electrodes, equivalent to the ring electrodes of a conventional ion-mobility spectrometer. One- on-one comparison in terms of performance was evaluated between a conventional stacked ring set-up and the flexible PCB set-up. Its analytical capability was demonstrated with the determination of the C12, C14 and C16 benzalkonium ions (BACs) in commercial cleaning products. The fourth project was the development and construction of an ion shutter which is the key factor in an ion mobility spectrometer. The ion shutter controls the injection of pulses of ions into the drift tube. A very short injection time is required to achieve high resolution. Theoretically, ion shutters depend on the design of suitable electronic circuits to create a narrow pulse for the ion injection. A new design of circuitry for pulse generation applicable for an ion mobility spectrometer is reported. The design is based on an optocoupler for the gate or through the trimmer resistor, for switching a pulse with amplitude of 40-70 V at high voltage up to 10 kV. The optocoupled pulser was compared to those of MOSFET-based pulser by comparison of the detection of tetraalkylammonium ions. To the best of our knowledge, this is the first use of an optocoupler-based pulser for ion injection in the ion mobility spectrometer. The fifth project was the coupling of a plasma source to an ion mobility spectrometer for direct testing of pharmaceutical tablets. The miniature plasma source is mounted at an oblique angle at the injection gate of the ion mobility spectrometer. A helium plasma is created by using a high alternating voltage of 8 kV at 28 kHz and is employed for the desorption and ionization of solid or liquid samples, which are placed on an electrically isolated sample holder. The instrument was built in-house at low cost and with a design that can be easily constructed by other laboratories. The instrument was tested with the rapid identification of drugs in pharmaceutical tablets such as acetaminophen, caffeine, loratadine, norfloxacin, tadalafil, and thiamine. The sixth project was the application of an ion mobility spectrometer coupled with an electrospray ionization source for the determination of the antibiotic tobramycin in ophthalmic solution. This method allows the direct analysis of tobramycin in the solution. The ion mobility spectrometry uses the developed printed circuit board as the drift tube. In order to ensure that the benzalkonium ions used as preservative in the sample did not interfere with the tobramycin detection a solution of benzalkonium salts was also measured using the electrospray – ion mobility spectrometer. To the best of our knowledge, this is the first time of the ESI-IMS for direct determination of tobramycin in eye drops. The last project was the determination of the ethylene gas by ion mobility spectrometry in combination with a Krypton lamp as photoionization source. Such a UV lamp with a specific excitation energy of 10.6 eV, the ethylene can be selectively ionized for measurement. The device makes use of stacked printed circuit board material for the construction of the drift tube, which can be easily built in-house. The effect of a field strength and a flow rate of drift gas on the peak area and resolving power of ethylene peak was investigated. One possibility of interference, which was ethanol, was studied for possible overlapping of the peaks. The novel method was developed and validated for ethylene gas liberated from five fruits. i.e. apples, avocados, bananas, kiwi fruit and pears. The analysis time was 20 s for one measurement.