Abstract

Compounds in crude oil are photoactive and can be toxic to marine ecosystems. However, chemical characterisation of crude oil poses a significant analytical challenge owing to its complexity. This challenge is further exacerbated by the photodegradation of crude oils in the environment. The aim of the work herein was to first isolate and characterise targeted fractions from crude oil and then assess the fractions after photodegradation, to better understand the composition of crude oil and photochemical transformation of individual chemical classes.Isolation of target fractions was achieved by validating a solid phase extraction (SPE) method using ion exchange SPE to fractionate Alaska North Slope (ANS) oil into discrete chemical classes. The SPE stationary phases used were strong cation exchange, strong anion exchange, and silica. Once the ANS oil was fractionated, chemical characterisation was complete using gas chromatography-mass spectrometry (GC-MS) and subsequently comprehensive two-dimensional gas chromatography-mass spectrometry (GCxGC-TOFMS) following analytical method development. Fractions were then subject to photodegradation using an accelerated weathering chamber with a xenon lamp.Chemical analysis of the fractions revealed the limitations of GC-MS when analysing crude oil. Many of the fractions, despite reduced complexity compared to the whole oil, exhibited unresolved complex mixtures (UCM). A method was developed for GCxGC-TOFMS where five column sets with varying film thickness, stationary phase, bleed line flow, modulation period, fill/flush time, sample loop length, and primary/secondary flow rates were tested to identify the columns that provided the best separation of compounds in each fraction. This method development led to successful characterisation of fractions containing dibenzothiophenes, fluorenes, fluorenones, sulfides, and xanthones.The experimental conditions of the photodegradation resulted in an excessive loss of mass. Analysis of the fractions showed that the photodegradation procedure was partially successful following the identification of a few photochemical transformation products including sulfoxides to sulfones, DEHP to MEHP, the formation of ketones, and possible conversion of xanthone to fluoren-9-one. Overall, the results show that the method developed for the fractionation and characterisation of the ANS crude oil was successful for the structural identification of individual chemical classes pre- and post-photodegradation. Future research would require optimisation and validation of the photodegradation experiment to avoid excessive evaporative losses and ensure environmental relevance.

Document Type

Thesis

Publication Date

2025

Embargo Period

2025-06-04

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

Download

Share

COinS