ANALYSIS OF OILS USING FLUORESCENCE.
25
or 355 nm ultraviolet excitation.
82 Studies by several groups have concentrated on the
development of remote fluorosensors capable of measuring both emission spectra and
fluorescence lifetimes,
11, 83 of crude oils on sea/water surfaces.
14, 84, 85, 86, 87
The
photochemical weathering of crude oils on water can be monitored using fluorescence
intensity, where there is a sharp decrease in intensity upon solar irradiation.
8, 88, 89
However, this decrease in intensity is probably due to light faction loss by evaporation
rather than the formation of any oxygenated species. The fluorescence intensity of crude
oils is extremely sensitive to the alkane concentration, and any loss will result in large
changes in fluorescence intensity.
10, 32
Chemometric methods such as Principal
Component Analysis (PCA) have been applied with fluorescence emission spectroscopy
to demonstrate the potential discrimination of oils types and weathering effects.
90
Computational models for discriminating or matching oil types vary from simple vector
models
91 to more complex Artificial Neural Networks.
92, 93 ANN methods have also been
used to help separate fluorescence signals from oil and humic substances in seawater.
94
7. APPLICATIONS: SUNDRY TECHNIQUES
Asphaltene aggregation was studied by front surface fluorescence spectroscopy,
95
and the use of fluorescence depolarisation (FD) techniques have been shown to
differences in asphaltene isolation methods,
96 measure asphaltene size,
97, 98, 99 and to track
the effect of temperature.
100 Khorasani and Michelsen,
101 used PCA and fluorescence
spectroscopy to derive a discrimination method for the assessment of maturity and oil
generation from marine algal kerogens. The use of fluorescence to study the impact of
crude oils on the environment is also becoming more important. Various fluorescence
methods have been used to look at the Polycyclic Aromatic Hydrocarbon (PAH) content
of crude oils and petroleum products,
102 and to characterise petroleum contaminated
soils
103 and the formation of oil-mineral aggregates.
104 Fluorescence techniques have also
been used to measure crude oil contamination in offshore sediments
105, 106 and the
formation of oil in water emulsions is also studied by fluorescence.
107 There have been
studies on estimating hydrocarbon levels in benthic organisms.
108 Fluorescence methods
were also used to study the cracking kinetics of crude oils at high temperatures and
pressures using a diamond anvil cell.
109 Time-resolved fluorescence spectra (plotted as
contour maps) have also been proposed as a method for discriminating different oil
types.
110, 111 The method, based on 250 nm laser excitation, shows potential, but as yet no
quantitative reports have been shown.
8. CONCLUSIONS
The use of fluorescence spectroscopy in a wide variety of methodologies for the
characterization and analysis of crude petroleum products is well established. Yet there
are still considerable opportunities for the development of robust, accurate, and
quantitative fluorescence methods for crude oil analysis. The rapid miniaturization and
increasing capability of fluorescence instrumentation is further expanding the range of
applications, particularly with regard to on-site and in-situ measurements. However, the
wide range of compact, portable excitation sources now available, presents a problem to
the crude oil fluorescence community. This diversity of excitation sources, each of
25
or 355 nm ultraviolet excitation.
82 Studies by several groups have concentrated on the
development of remote fluorosensors capable of measuring both emission spectra and
fluorescence lifetimes,
11, 83 of crude oils on sea/water surfaces.
14, 84, 85, 86, 87
The
photochemical weathering of crude oils on water can be monitored using fluorescence
intensity, where there is a sharp decrease in intensity upon solar irradiation.
8, 88, 89
However, this decrease in intensity is probably due to light faction loss by evaporation
rather than the formation of any oxygenated species. The fluorescence intensity of crude
oils is extremely sensitive to the alkane concentration, and any loss will result in large
changes in fluorescence intensity.
10, 32
Chemometric methods such as Principal
Component Analysis (PCA) have been applied with fluorescence emission spectroscopy
to demonstrate the potential discrimination of oils types and weathering effects.
90
Computational models for discriminating or matching oil types vary from simple vector
models
91 to more complex Artificial Neural Networks.
92, 93 ANN methods have also been
used to help separate fluorescence signals from oil and humic substances in seawater.
94
7. APPLICATIONS: SUNDRY TECHNIQUES
Asphaltene aggregation was studied by front surface fluorescence spectroscopy,
95
and the use of fluorescence depolarisation (FD) techniques have been shown to
differences in asphaltene isolation methods,
96 measure asphaltene size,
97, 98, 99 and to track
the effect of temperature.
100 Khorasani and Michelsen,
101 used PCA and fluorescence
spectroscopy to derive a discrimination method for the assessment of maturity and oil
generation from marine algal kerogens. The use of fluorescence to study the impact of
crude oils on the environment is also becoming more important. Various fluorescence
methods have been used to look at the Polycyclic Aromatic Hydrocarbon (PAH) content
of crude oils and petroleum products,
102 and to characterise petroleum contaminated
soils
103 and the formation of oil-mineral aggregates.
104 Fluorescence techniques have also
been used to measure crude oil contamination in offshore sediments
105, 106 and the
formation of oil in water emulsions is also studied by fluorescence.
107 There have been
studies on estimating hydrocarbon levels in benthic organisms.
108 Fluorescence methods
were also used to study the cracking kinetics of crude oils at high temperatures and
pressures using a diamond anvil cell.
109 Time-resolved fluorescence spectra (plotted as
contour maps) have also been proposed as a method for discriminating different oil
types.
110, 111 The method, based on 250 nm laser excitation, shows potential, but as yet no
quantitative reports have been shown.
8. CONCLUSIONS
The use of fluorescence spectroscopy in a wide variety of methodologies for the
characterization and analysis of crude petroleum products is well established. Yet there
are still considerable opportunities for the development of robust, accurate, and
quantitative fluorescence methods for crude oil analysis. The rapid miniaturization and
increasing capability of fluorescence instrumentation is further expanding the range of
applications, particularly with regard to on-site and in-situ measurements. However, the
wide range of compact, portable excitation sources now available, presents a problem to
the crude oil fluorescence community. This diversity of excitation sources, each of