Near-Infrared Spectroscopy Coupled with Multivariate Methods for the Characterization of Ethanol Adulteration in Premium 91 Gasoline

Abstract

Ethanol, as a result of its high octane rating of 108, is often added as adulterant to premium 91 gasoline fuels to boost up their octane ratings to 96 or more, but it does not provide the same power to the engine as that of superpremium 96 gasoline fuels. In this study, sensitive near-infrared spectroscopy (NIRS) coupled with chemometrics was proposed for analysis of the ethanol content in premium 91 gasoline fuels. Standard samples of premium 91 octane gasoline were collected from Oman Oil Refineries and Petroleum Industries Company commonly known as ORPIC. The premium 91 samples were then intentionally spiked with ethanol at various levels. NIRS was employed in the absorption mode to obtain the spectra of all samples scanning from 700 to 2500 nm. Then, partial least squares regression (PLSR), partial least squares discriminant analysis (PLS-DA), and principal component analysis (PCA) were applied to model and interpret the near-infrared (NIR) spectra. A PLS-DA model was developed to discriminate between the pristine gasoline samples and those intentionally mixed with ethanol, with excellent results [R2 = 98% and root-mean-square error (RMSE) = 0.049%] by random cross-validation. A PLSR model was established to determine the ethanol content in premium 91 gasoline samples, with values of R2 = 99% and root-mean-square error of cross-validation (RMSECV) = 1.88% and R2 = 99% and root-mean-square error of prediction (RMSEP) = 1.58 for cross-validation and test-set validation results, respectively. This newly developed method is simple and rapid and can quantify less than 2% ethanol adulteration in premium 91 gasolines.