# Raman Spectroscopy and 2 DCOS Analysis of Unsaturated Fatty Acid in Edible Vegetable Oils
## 2 Experiment  
Seven edible vegetable oil samples (A-G) and three types of unsaturated fatty acids (oleic acid, linoleic acid, and \(\alpha\)-linolenic acid) were investigated. Sample A is Golden Dragon Fish sunflower seed oil. Samples B and C are corn oils of the Fortune and Golden Dragon Fish brands, respectively. Sample D is Luhua peanut oil. Samples E, F, and G are extra virgin olive oils of the Huilerie Loued, Olivoila, and Luhua brands, respectively. These samples were purchased from standard supermarkets in Wuhan. The oleic acid (OA), linoleic acid (LA) and \(\alpha\)-linolenic acid (ALA) samples were purchased from MOLBASE. All the samples were used as received without further treatment. Table 1 lists the MUFA, PUFA, and saturated fatty acid content in the samples A-G, which were declared by the producers of these samples. The stated purities of the OA, LA, and ALA are 98.5%, 97%, and 97%, respectively.  
Raman spectra of the samples were obtained in backscattering configuration with a Nanobase XperRam200 microprobe spectrometer. The excitation source was a 532 nm green laser. The samples were placed in glass flasks. The laser spot on the sample was about two micrometers. The laser power on sample was varied up to 5 mW to check the laser power's influence on the Raman spectral features of the samples, which indicated that laser heating or damage of the samples was negligible in our experiment. The scattered signal was detected by an air-cooled CCD detector. The spectral resolution is about 1.5 cm\({}^{-1}\) with 1800 lines/mm grating. All the spectra were recorded at room temperature of about 25 \({}^{\circ}\)C, with 15 s acquisition time and 2 scan average. For wavenumber calibration, a Si substrate was measured first, then the system was calibrated using the 521 cm\({}^{-1}\) phonon mode of Si as reference. The Si spectrum was also measured after experiments to ensure the calibration was not changed during  
\begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **MUFA (\%)** & **PUFA (\%)** & **Saturated Fatty Acid (\%)** \\ \hline A & 26 & 61 & 13 \\ \hline B & 30 & 56 & 14 \\ \hline C & 32 & 53 & 15 \\ \hline D & 44 & 38 & 18 \\ \hline E & 75 & 10 & 15 \\ \hline F & 78 & 7 & 15 \\ \hline G & 79 & 6 & 15 \\ \hline \end{tabular}
\end{table}
Table 1: The monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), and saturated fatty acid content in the samples A–G.  
the measurements. For each sample, 5 random spectra were measured and the average spectrum was used for the analyses of relative intensity ratios.  
The synchronous and asynchronous 2D spectra were calculated using the software 2D Shige. The baseline of raw Raman spectrum was corrected using Origin Pro 8.0 program. The baseline correction was performed with subtraction of a polynomial curve of the raw Raman spectrum, the main feature of the raw Raman spectrum is kept with this treatment, especially in the spectral range of 1200-1800 cm\({}^{-1}\). The baseline corrected data was put into the 2D Shige software with increasing MUFA content (or decreasing PUFA content). The calculated result was replotted in Origin for better visualization.