Interpretation of UV ion mobility spectra by coupling to time of flight mass spectrometry

Abstract

As shown by theoretical and experimental results in this thesis, a carefully designed UV-IMS[PID] coupling with oa-TOFMS was successfully self set up. It offers high transmission, simple spectrum, high speed and it is able to record the whole mass spectrum quasi simultaneously. These features make it attractive to identify ions, fragments or ion clusters in IMS and to conduct high-throughput molecular analysis of large libraries for compound confirmation and purity assessment. By simulation with SIMION v. 7.0 it was proved that the configuration of the three stage differential pump system and the Einzel lens was suitable for an orthogonal design of an interface between atmospheric pressure and the TOFMS. The pinhole interface system to the UV-IMS [PID]-TOF was characterized by studying a two and a three stage interface. They are optimized and proved to be able to identify ions that has been ionized in IMS.This device has been proved to have unique benefits for volatile organic compounds analysis. The detection limits are in the range of 0.8 µg/L for acetone, 8.6 µg/L for ethanol and 17.2 µg/L for benzene with direct permeation sampling. The instrument has a dynamic range of about 3 decades for all detected compounds. A wide range of applications including chemical weapon simulation substances detection as well as fungal analysis were achieved with this device. It yields simple spectra that facilitate analysis. Compared the results of TOF spectra with UV-IMS spectra, most VOCs appearing in UV-IMS are monomer or protonated monomer ions. For the selected ketones from acetone to nonanone, the most abundant ions are protonated molecular ions and beginning from hexanone, the fragmentation is evident and can be detected in IMS. In the case of selected alcohols, not all of them have base peak corresponding to protonated molecule ions. Some of them such as 3-methyl-2-butanol and 2-hexanol the fragment ion are most abundant. These two groups of compounds all have obvious water adducts peaks because of high proton affinities. For aromatic substances the major ion is the molecular ion.