957
10
300
Kx (nm)
RS
ater
70
RS
500
3)
arious excitation
c/5
o I 1 1 L—» IIILh
300 350 400 450 350 400 450 500
Wavelength (nm)
Figure 3 : Fluorescence spectra of Libyan crude oil dispersed in water with various excitation
wavelengths.
3 - SPECTRAL FEATURES OF OIL DISPERSED IN WATER AND TECHNIQUE
FOR SEPARATION OF ITS FLUORESCENCE
We want to mar k out some very interesting features of fluorescence spectra for oils dispersed
in water. In that experiment fluorescence spectra were detected using several close excitation
wavelengths. In Fig. 3a and 3b we can see fluorescence spectra of dispersed in water Libyan crude
oil with excitation at 300...315 nm and 325...345 nm As one could see in Fig. 3a, changes of
excitation wavelength for 5... 15 nm lead to essential decreasing of fluorescence intensity at
wavelength 340 nm, but the intensity of fluorescence in longwave part of spectrum is practically
constant. Similar changes in fluorescence spectral shape one could see in Fig. 3b with excitation at
325...345 nm; the fluorescence decreasing could be seen at 360 nm Such spectral behaviour leads
us to conclusion that fluorescence band for oils dispersed in water consists of at least three
components: with maxima at 340, 360 nm and near 400 nm We mark out that using only one
excitation wavelength from above mentioned spectral region 300...345 nm does not permit to
observe the multicomponent structure of oil fluorescence spestrum.
We can compare fluorescence spectra with different excitation wavelengths for oil in water
and for natural dissolved organic matter. The spectral behaviour for natural DOM with Xex
alteration is very unusual for organic compounds. While excitation wavelength is less than some
wavelength limit (approximately 340 nm) ftmax for DOM spectra is practically constant, the
variation of maximum location does not exceed 10 nm But with increasing of ilex above 340 nm,
spectral maximum shifts to longer wavelengths, so that difference between ftex and ft max is nearly
constant and not less than 80 nm
