10
A. G. RYDER
3.2. Time-Resolved Fluorescence
Figure 7. Variation of fluorescence decay time with emission wavelength for several crude oils. Data was
collected with 337 nm excitation and using a single exponential fitting approach. Reproduced with permission
from Ref [16], © 1974, Optical Engineering.
The fluorescence lifetime of crude oils is very sensitive to composition, with heavy
oils having shorter lifetimes than light oils (Figure 7).
10, 16, 21, 22, 25 The 1974 study also
showed a positive correlation between API gravity for four crude oils, and the decay time
being measured at max . The changes in fluorescence lifetime is a result of the interplay
between energy transfer and quenching, and is also emission wavelength dependant,
since each emission wavelength represents a different population of emitting
fluorophores. The numerical value of the fluorescence lifetime is however, very
dependant on the method by which it is calculated. In Figure 7, the lifetimes were
calculated via a single exponential convolution process, which should not be used other
than for the most qualitative of descriptions. Rayner and Szabo,
20 used Time Correlated
Single Photon Counting (TCSPC) with a pulsed nitrogen lamp source to measure
fluorescence lifetime data from a series of 13 oils, including five crude oils. They
calculated lifetime values via a deconvolution method, the fitting of two decay terms, and
the requirement that the residuals of the fit be randomly distributed about zero. This
resulted in reproducible fits with three parameters being reported: a , b , and F a /F b , with
F a /F b being the ratio of the pre-exponential factors for the two lifetime components.
A. G. RYDER
3.2. Time-Resolved Fluorescence
Figure 7. Variation of fluorescence decay time with emission wavelength for several crude oils. Data was
collected with 337 nm excitation and using a single exponential fitting approach. Reproduced with permission
from Ref [16], © 1974, Optical Engineering.
The fluorescence lifetime of crude oils is very sensitive to composition, with heavy
oils having shorter lifetimes than light oils (Figure 7).
10, 16, 21, 22, 25 The 1974 study also
showed a positive correlation between API gravity for four crude oils, and the decay time
being measured at max . The changes in fluorescence lifetime is a result of the interplay
between energy transfer and quenching, and is also emission wavelength dependant,
since each emission wavelength represents a different population of emitting
fluorophores. The numerical value of the fluorescence lifetime is however, very
dependant on the method by which it is calculated. In Figure 7, the lifetimes were
calculated via a single exponential convolution process, which should not be used other
than for the most qualitative of descriptions. Rayner and Szabo,
20 used Time Correlated
Single Photon Counting (TCSPC) with a pulsed nitrogen lamp source to measure
fluorescence lifetime data from a series of 13 oils, including five crude oils. They
calculated lifetime values via a deconvolution method, the fitting of two decay terms, and
the requirement that the residuals of the fit be randomly distributed about zero. This
resulted in reproducible fits with three parameters being reported: a , b , and F a /F b , with
F a /F b being the ratio of the pre-exponential factors for the two lifetime components.