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Analysis of polycyclic aromatic hydrocarbons by chemical ionization and ion trap mass spectrometry

University of British Columbia

The aim of this thesis is to develop and explore the use of novel mass spectrometric techniques for the isomer specific analysis of PAHs and the detection of PAH transformation products in environmental samples. The first objective was achieved by using chemical ionization (CI) mass spectrometric techniques. Negative CI with CO₂ and N₂O as reagent gases resulted in the formation of isomer specific adducts, such as [M + G – H]⁻, between PAH molecules (M) and gas phase negative ions (G), enabling the differentiation of several PAH structural and positional isomers. In positive chemical ionization mode, on a linear quadrupole mass spectrometer, isomer differentiation was obtained with dimethyl ether (C₂H₆O) as a reagent gas. However, the same results could not be generated using an ion trap mass spectrometer. Consequently, other chemical ionization reagents were investigated for their potential to differentiate PAH isomers in an ion trap. Halogenated hydrocarbons, such as CH₂Cl₂ and CH₃CHF₂, proved to be the most successful chemical ionization reagents for this task. These substances formed adduct ions of the type [M + R]⁺ and [M + R - HX]⁺ (M = PAH molecule, R = reagent ion and X = Cl or F). Isomer identification was possible based on variations in the type and abundance of adducts formed. Application of these chemical ionization techniques to a contaminated environmental sample enabled the differentiation of several PAH isomers, including alkyl substituted ones. Differentiation of PAH isomers was also achieved through the use of ion/molecule reactions with mass-selected fluorocarbons, such as C₃F₅⁺, generated from the electron ionization of perfluorotributylamine (FC43). The second objective, the analysis of PAH transformation products, was achieved via GC/MS/MS experiments in an ion trap mass spectrometer. By using optimized collision induced dissociation conditions, several polyaromatic quinones that were undetectable by standard GC/MS analyses, were identified in a contaminated sediment sample collected from an aluminum smelter effluent lagoon.

Thesis/Dissertation

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2009-06-24

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http://hdl.handle.net/2429/9571

Chemistry

University of British Columbia

UBCV

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