Advanced separation techniques combined with mass spectrometry for difficult analytical tasks – isomer separation and oil analysis

Abstract

This thesis covers two aspects of utilisation of advanced separation technology together with mass spectrometry: 1. Drift tube ion mobility spectrometry – mass spectrometry (IMS-MS) studies of the behaviour of ions in the gas phase and 2. Comprehensive two dimensional gas chromatography – time-offlight mass spectrometry (GC×GC-TOF-MS) studies for characterization of crude oil samples. In IMS studies, the focus was on the separation of isomeric compounds. For example, [M-H]- ions of 2,4-di-tert-butylphenol (2,4-DtBPh) and 2,6-di-tert-butylphenol (2,6-DtBPh) were separated. It was also observed that shielding of the charge site by the functional groups of a molecule has a large effect on the separation of the isomeric compounds. For example, amines with a shielded charge site were separated from those with a more open charge site, while some of the isomeric amines studied were not separated. Different kinds of adduct ions were observed for some of the analytes. Dioxygen adducts were seen for 2,4-DtBPh [M+O2]-, 2,6-di-tert-butylpyridine (2,6-DtBPyr) [M+O2]+· and 2,6-di-tert-butyl-4-methylpyridine (2,6-DtB-4MPyr) [M+O2]+·. The adduct formation increases the total mass of the analyte ion, and therefore, for example the 2,4-DtBPh [M+O2]- ion could be separated from its isomeric compound 2,6-DtBPh [M-H]-, which did not from the dioxygen adduct ion. In the case of 2,6-DtBPyr and 2,6-DtB-4MPyr, the [M]+ ions formed dioxygen adduct [M+O2]+· ions. The both ions, [M]+ and [M+O2]+·, shared the same drift time which was longer than their [M+H]+ ion species. This work demonstrates that measuring with IMS the mobility of different ion structures of the same molecule, especially dioxygen adducts, results in a better understanding of the role of adduct ions in the IMSseparation process. In GC×GC-TOF-MS studies, the focus was on detailed characterization of crude oil samples. For instance, oils from the Recôncavo Basin were classified to two different groups by using minor oil components. The GC×GC-TOF-MS data showed the correlation between 2D retention time and the number of carbons in a ring for several hydrocarbons as known from the literature. This information was used to achieve more structural information about eight new tetracyclic compounds, some of them similar to nor-steranes, detected during analysis. Some of these new compounds could be used as maturity indicators. This study demonstrated how GC×GC-TOF-MS can be used to separate geochemically interested isomers, identify minor geochemical differences between oils and achieve structural information about unknown biomarkers