Geoscience Reference
In-Depth Information
∆λ
= 20nm
∆λ
= 40nm
∆λ
= 60nm
200 300 400
500 600 700
Wavelength (nm)
Figure 3.13. Synchronous fluorescence spectra of treated sewage effluent at 20 nm, 40 nm, and 60 nm
offset values (Δ
λ
). (Adapted from Galapate et al.,
1998
, with permission from Elsevier.)
For SFS, fluorescence intensities can be expressed as
I
f
=
ηI
a
, where
η
is the quantum
yield at
λ
ex
and
I
a
is the absorbed intensity (Reynolds and Ahmad,
1995b
). From Beer's law,
I
a
=
I
0
{
1
- exp(-
αcl
)}, where
I
0
is the incident intensity,
α
is the absorption cross section
and
l
is the effective sampling length. For
αcl<<l, I
f
≈ I
0
ηcl
. In SFS the excitation wave-
length (
λ
ex
) and the emission wavelength (
λ
em
) are scanned synchronously, with a fixed
off-set such that △
λ
= (
λ
em
-
λ
ex
). The normalized fluorescence intensity can be represented
by:
I
f
/I
0
=
I
0
λ΄ α
(
λ΄
)
cl
, where the quantum yield and the absorption cross-section are func-
tions of
λ΄
= (
λ
em
- △
λ
). The intensity distribution will, therefore, show a pronounced peak
when the absorption maximum and the quantum yield maximum overlap. For well defined
