New applications and developments of field-asymmetric ion mobility spectrometry - mass spectrometry (FAIMS-MS)

Field asymmetric ion mobility spectrometry (FAIMS), also commonly termed differential mobility spectrometry (DMS), is a gas-phase ion separation technology. FAIMS exploits differences in high-electric-field to low-electric-field ion mobility ratios to discriminate between ion species. FAIMS and mass spectrometry (MS) provide generally orthogonal ion separation and are easy to interface. One of the most attractive benefits of FAIMS in conjunction with MS is its ability to remove nondescript chemical noise as well as particular interferents from an ion population. This generally increases the sensitivity of MS analyses. Also, in contrast to most known separation techniques, FAIMS transmits analytes continuously rather than in pulsed or peak fashion. This quality is advantageous in structural elucidation studies by tandem MS.

So far, FAIMS has been used for proteomics-related studies (identification of tryptic peptides), separation of protein conformers, identification of drinking water contaminants, detection of chemical warfare agents and volatile organic compounds in air, separation of various isomers, improving LC-MS analyses of pharmaceuticals, and more. The objective of this thesis is to explore new applications along with new embodiments of FAIMS instrumentation.

First, the successful separation and sensitive quantification of enantiomers in FAIMS by complexation with chiral reference compounds is demonstrated for six amino acids and the drug terbutaline. Second, the role of clusters in inducing unwanted complexity in FAIMS compensation voltage spectra is investigated. Such clusters are characterised and strategies to minimise their disturbing impact are suggested. Third, in a different application, triazine herbicides and some of their metabolites are quantified with FAIMS-MS. This project ultimately aims at the coupling of membrane extraction techniques to ESI-FAIMS-MS. Fourth, a new FAIMS interface is designed to display a strong ion focusing effect, thus allowing for a wide open axial ion inlet and increased ion transmission, compared to existing FAIMS designs. The new interface is treated experimentally and theoretically.

In the introduction to the thesis, the FAIMS theory is summarised. FAIMS is compared to other separation techniques, the ways in which FAIMS augments atmospheric pressure ion optics are discussed, and a review of some FAIMS applications is given.