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Introduction Figure 1.5: HPLC Chromatogram from a typical SARA analysis. The bold line represents the RI signal, while the thin line represents the UV signal at 254nm. The maxima of the aromatic and resin peaks are cut for better visualisation. Reproduced from [35]. In the case of complex mixtures covering a broad range of molecular weights and polarity, currently available chromatographic methods often have some limitations. Problems can arise from inadequate resolving power, low volatility, low solubility of the components in the chromatographic mobile phase, strong adsorption of sample components on the stationary phase, or low detector sensitivity. Thus, no single HPLC method can be utilised for all types of crude oils so specific methods must be developed. A particular crude oil may need specific solvents, detectors and columns [16]. Because of these limitations of HPLC, the OCLC method is still used regularly for the analysis of crude oils, particularly when separations of large quantities are required [33]. 12
1.2 Fluorescence Spectroscopy 1.2.1 Fluorescence Introduction If a molecule is promoted to an electronically excited state by the absorption of ultraviolet, visible, or near infrared radiation, luminescence or the emission of light from this state can occur when this excited molecule decays back to the ground state, or to a lower-lying excited electronic state [36]. Luminescent processes are subdivided into fluorescence and phosphorescence. The key characteristic of fluorescence spectroscopy is its high sensitivity, achieving limits of detection several orders of magnitude lower than many other analytical techniques. Limits of detection of 10 −10 M or lower are possible for intensely fluorescent molecules. Under controlled conditions, single molecule (the ultimate limit of detection) may be reached. Be- cause of the low detection limits, fluorescence is widely used for quantification of trace constituents of biological and environmental samples [37]. Also the use of fluorescent molecules or markers to detect non-fluorescent molecules is widespread and has numerous applications (such as molecular imaging and DNA sequencing) [38]. Fluorescence can be considered as a three-stage process that is best illustrated by a Perrin-Jablonski diagram (Figure 1.6 [36, 38]). Stage 1: Excitation Following light absorption, a molecule is excited from the ground state to one of the vibrational levels of an upper excited electronic state (S1 or S2). This is shown as a vertical transition which occur in the 10 −15 s time frame, too short to significantly displace the nuclei (the Frank-Cordon principle [39]) or change the electronic spin-state from that of the ground state configuration. Stage 2: Excited-State Transitions The S1 or S2 excited state exists for a finite time with a subsequent partial dissipation of energy in the form of heat by rapid relaxation to the lowest vibrational level of S1 , yielding a relaxed singlet excited state (S1) from which fluorescence emission originates. This process is called internal conversion and occurs in 10 −12 s or less. Since fluorescence lifetimes are typically near 10 −9 s, internal conversion is generally complete prior to emission. Not all the molecules initially excited by In a few rare exceptions emission occurs from the S2 excited state e.g. Azulene. 13
Page 1 and 2: Time-Resolved Fluorescence Spectros
Page 3 and 4: Abstract behaviour allowing calcula
Page 5 and 6: Contents List of Publications and P
Page 7 and 8: Contents 2.3 Temperature based Life
Page 9 and 10: List of Publications and Presentati
Page 11 and 12: Abbreviations Abbrev Definition API
Page 13 and 14: Chapter 1 Introduction For many yea
Page 15 and 16: Introduction temperature increases
Page 17 and 18: A seal or cap-rock that prevents th
Page 19 and 20: Introduction Figure 1.2: Crude oil
Page 21 and 22: Introduction eroatoms (O, S, N) and
Page 23: Introduction toluene, dichlorometha
Page 27 and 28: Introduction S1 state for a certain
Page 29 and 30: Introduction The peaks in the absor
Page 31 and 32: Introduction Figure 1.9: Jablonski
Page 33 and 34: Introduction Figure 1.10: Static qu
Page 35 and 36: Introduction the ratio of τ 0/τ i
Page 37 and 38: 1.2.5 Measuring fluorescence lifeti
Page 39 and 40: Introduction Figure 1.14: Time-reso
Page 41 and 42: Introduction The autocorrelation fu
Page 43 and 44: Introduction case, the molecules ex
Page 45 and 46: From Equation 1.26, Introduction ω
Page 47 and 48: m = 1 P 2 + Q 2 Introduction (1.36
Page 49 and 50: Introduction based average lifetime
Page 51 and 52: Introduction Figure 1.21: General p
Page 53 and 54: Introduction TAC output pulse is gi
Page 55 and 56: Introduction at each frequency acco
Page 57 and 58: Introduction diagram showing the op
Page 59 and 60: Introduction Figure 1.26: Schematic
Page 61 and 62: Introduction provides enhanced cont
Page 63 and 64: Introduction PAH’s. It has been s
Page 65 and 66: to heavy oils (low API gravity). In
Page 67 and 68: Introduction The balance between en
Page 69 and 70: Introduction Figure 1.34: Fluoresce
Page 71 and 72: Introduction used [126, 129, 132] a
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fractional contributions over time
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Introduction concentration and Ksv
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Introduction Figure 1.38: Fluoresce
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Introduction Figure 1.39: Fluoresce
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1.5 Crude oil photophysics Introduc
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Introduction stages of thermal matu
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Introduction yellow to red fluoresc
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1.7 Thesis goal Introduction This i
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Materials and Methods concentration
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Table 2.2: Fractionation Data for B
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Materials and Methods 2.2 Frequency
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Materials and Methods was within ±
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Materials and Methods The dichroic
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Figure 2.5: Transmission characteri
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Materials and Methods Figure 2.7: S
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Materials and Methods The variation
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Materials and Methods Figure 2.9: L
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Materials and Methods Figure 2.10:
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Materials and Methods Comparison ca
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Materials and Methods with ρ param
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Materials and Methods 2.3 Temperatu
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Materials and Methods IRF of the sy
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Materials and Methods 2.4 Temperatu
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Materials and Methods a series of w
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Materials and Methods 2. Using the
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Lifetime study on crude oils by the
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Table 3.3: Average lifetime and sin
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Table 3.5: Average lifetime and sin
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3.5 Single Lifetime distributions L
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Energy Transfer and Quenching proce
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Influence of low temperature on flu
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Conclusions and Future Work model (
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Appendix A Reference Lifetime Stand
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Appendix Figure A.2: FD response fo
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A.3 SPA N-(3-sulfopropyl) acridiniu
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A.4 Rhodamine B Appendix Rhodamine
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A.5 Acridone Appendix The highly ph
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Appendix Figure A.11: FD response f
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Table B.1: Frequency Domain average
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Appendix Table B.3: Emission λmax
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Table B.5: Frequency Domain lifetim
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Appendix for the determination of t
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Appendix Figure C.3: Multifrequency
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Appendix Figure C.5: FLIM intensity
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Appendix Table C.1: Fluorescence li
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Appendix D Published Work 281
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998 J Fluoresc (2008) 18:997-1006 s
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1000 J Fluoresc (2008) 18:997-1006
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1002 J Fluoresc (2008) 18:997-1006
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1004 J Fluoresc (2008) 18:997-1006
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1006 J Fluoresc (2008) 18:997-1006
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Bibliography [10] W. G. Dow (1977),
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Bibliography [31] M. A. Ali and W.
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Bibliography [53] R. D. Spencer and
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Bibliography [75] K. Konig (2000),
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Bibliography [93] C. Pasquini and A
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Bibliography [113] C. Ralston, X. W
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Bibliography [132] A. Ryder (2004),
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Bibliography variable-angle synchro
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Bibliography [171] R. K. McLimans (
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Bibliography using fluorescence spe
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Bibliography [210] H. Mishra, S. Pa
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Bibliography [229] N. Boens, W. W.
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