ANALYSIS OF OILS USING FLUORESCENCE.
23
Figure 18: FLEEMS measurements of inclusion showing optimum excitation and optimum emission spectra for each
inclusion. Excitation slit = 10 nm. Emission slit = 10 nm. Scanning speed = 60 nm per min. All spectra are normalized to same
fluorescence intensity level for ease of comparison. Measuring microscope objective: Olympus D Apo UV 100 x , N.A. 1.3 oil
immersion. Reproduced with permission from Ref. [76] © 1996, Elsevier Science Ltd
Coupling a standard steady-state fluorimeter to an epi-fluorescence microscope using
fibre optics enabled the collection of excitation, emission, and synchronous excitationemission from microscopic sample areas, such as single HCFI.
76
When the
monochromators are set to zero order it enabled the collection of the emission spectrum
at optimum excitation conditions, and the excitation spectrum at optimum emission
conditions (Figure 18). This methodology was used to discriminate different HCFI on
the basis of these spectra or via values extracted such as optimum excitation wavelength
or the Stokes shift. Kihle also demonstrates the collection of synchronous fluorescence
excitation-emission spectra from individual inclusions.
76
However, steady-state based fluorescence measurements for inclusions suffer from
several drawbacks (apart from those mentioned in section 4.1). The apparent
fluorescence intensity and spectral distribution can adversely be influenced by the
physical properties of the sample such as geometry, opacity, sample turbidity, and the
scattering properties of both the actual inclusion and host mineral. The last factor is
particularly important in the context of HCFI studies where there is a large variation in
sample type. Photobleaching of synthetic and natural HCFI has been shown to cause
changes in the fluorescence emission intensity.
61
In 1987, McLimans outlined the potential for using fluorescence lifetime
measurements for HCFI analysis.
67
He showed that fluorescence lifetime (355 nm
excitation) increased on going from condensate, to very mature, to moderately mature, to
immature oils. There was also a noticeable increase in lifetime for all oils with emission
wavelength over the 400-600 nm range. However, no data was provided on the method
for calculating fluorescence lifetime or about the chemical composition / source of the
oils samples, nor was any HCFI data presented.
23
Figure 18: FLEEMS measurements of inclusion showing optimum excitation and optimum emission spectra for each
inclusion. Excitation slit = 10 nm. Emission slit = 10 nm. Scanning speed = 60 nm per min. All spectra are normalized to same
fluorescence intensity level for ease of comparison. Measuring microscope objective: Olympus D Apo UV 100 x , N.A. 1.3 oil
immersion. Reproduced with permission from Ref. [76] © 1996, Elsevier Science Ltd
Coupling a standard steady-state fluorimeter to an epi-fluorescence microscope using
fibre optics enabled the collection of excitation, emission, and synchronous excitationemission from microscopic sample areas, such as single HCFI.
76
When the
monochromators are set to zero order it enabled the collection of the emission spectrum
at optimum excitation conditions, and the excitation spectrum at optimum emission
conditions (Figure 18). This methodology was used to discriminate different HCFI on
the basis of these spectra or via values extracted such as optimum excitation wavelength
or the Stokes shift. Kihle also demonstrates the collection of synchronous fluorescence
excitation-emission spectra from individual inclusions.
76
However, steady-state based fluorescence measurements for inclusions suffer from
several drawbacks (apart from those mentioned in section 4.1). The apparent
fluorescence intensity and spectral distribution can adversely be influenced by the
physical properties of the sample such as geometry, opacity, sample turbidity, and the
scattering properties of both the actual inclusion and host mineral. The last factor is
particularly important in the context of HCFI studies where there is a large variation in
sample type. Photobleaching of synthetic and natural HCFI has been shown to cause
changes in the fluorescence emission intensity.
61
In 1987, McLimans outlined the potential for using fluorescence lifetime
measurements for HCFI analysis.
67
He showed that fluorescence lifetime (355 nm
excitation) increased on going from condensate, to very mature, to moderately mature, to
immature oils. There was also a noticeable increase in lifetime for all oils with emission
wavelength over the 400-600 nm range. However, no data was provided on the method
for calculating fluorescence lifetime or about the chemical composition / source of the
oils samples, nor was any HCFI data presented.