3. Results and discussion
Raman spectra of pumpkin seed oil have been detected using
VIS Raman and UVR (panels (a) and (b) of Fig. 2, respectively). Using
488 nm for the excitation of the Raman scattering yields poor
spectra with strong fluorescence, while the use of the UV laser at
266 nm results in a nicely resolved, fluorescence-free spectrum.
Specifically, the n(C]C) stretching vibration mode of cis RHC ¼ CHR
at 1660 cm1 was resonantly excited by UVRR. This specific band is
a reliable measure for the degree of unsaturation and saturation of
fatty acids (Barthus & Poppi, 2001). Thus, it can be expected that
the UVRR results help to accurately predict the iodine value of oils
and fats (Lerner, Garry, & Walder, 1992). Besides this, the shift of
this band to higher wavenumbers is related to the change between
cis to trans fatty acids. We expect that UVR is also well suited for
petroleum analysis, where strong fluorescence prevents standard
Raman spectroscopy in the VIS. Intense UVRR spectra can there be
predicted also due to the absorption peak around 260 nm