A hard modeling approach to determine methanol concentration in methanol gasoline by Raman spectroscopy

The aim of this work is to establish a practical quantitative analysis technique to determine the methanol proportion in methanol–gasoline by using Raman spectroscopy and a hard modeling method. Three hydrocarbon gasoline samples coming from different refineries were added methanol with different concentrations to prepare 27 gasoline–methanol mixture samples with methanol concentration varying from 5% to 70%. Their Raman spectra ranging from 600 to 1800 cm−1 were collected. And then the hard modeling method and two soft methods, namely partial least squares (PLSs) and least squares support vector machine (LSSVM), were performed on the preprocessed spectra to determine methanol concentration. Experimental results show the root mean square error of prediction (RMSEP) based on hard modeling method was 1.02% (v/v), meanwhile that of PLS and LSSVM was 3.28% (v/v) and 3.10% (v/v), respectively. Therefore, the proposed hard modeling method can be particularly applied in complicated mixture samples with overlapping spectra and nonlinear characteristics.