Quantification of anhydrous ethanol and detection of adulterants in commercial Brazilian gasoline by Raman spectroscopy

Raman spectroscopy can be used to evaluate the quality of fuels in a remote, rapid, and nondestructive manner without the need for reagents. In this study, Raman was used to quantify anhydrous ethanol in commercial gasoline and to detect peaks due to compounds commonly used for the adulteration of commercial gasoline. Samples of commercial gasoline were collected from fuel stations in the region of Santos, SP, Brazil. Samples of naphtha from the refinery, pure ethanol, and ethanol diluted in distilled water at concentrations close to the range used in the gasoline were also obtained and characterized. Raman spectra were collected using a dispersive Raman spectrometer (830 nm, 2 cm(-1) resolution in the 400-1800 cm(-1) spectral range). As expected, the spectra of commercial gasoline showed pronounced peaks of naphtha and ethanol. By using the peak intensities of the ethanol diluted in water, the ethanol concentration was found to be in the range of 27% +/- 1% in most of the samples; some samples presented ethanol concentrations as high as 28.8%, suggesting adulteration. Some samples presented peaks at 766, 798, and 995 cm(-1) with higher intensities, suggesting the presence of an adulterant with organic characteristics, such as solvents with aromatic rings. Raman spectroscopy has been shown to be effective in determining the adulteration of commercial gasoline, which may contribute to rapid quality control of fuels at the point of sale.