Study on Rapid Quantitative Analysis Method of Methanol Content in Methanol Gasoline by Raman Spectroscopy and Partial Least Squares

Methanol gasoline is a new fuel to replace traditional gasoline, and its quality is greatly affected by methanol content. Therefore, the rapid analysis and detection of methanol content in methanol gasoline will have far-reaching significance for its quality control. A rapid quantitative analysis method of methanol content in methanol gasoline based on Raman spectroscopy and partial least squares (PLS) was established in this work. Raman spectra of 49 methanol gasoline samples were collected by laser Raman spectrometer, and spectral analysis was carried out. The effects of five spectral pretreatment methods on the raw Raman spectra of methanol gasoline were compared. In addition, variable importance in projection (VIP) was used to extract the Raman spectra's feature variables preprocessed by wavelet transform (WT). The number of latent variables (LVs) and VIP threshold of the PLS calibration model was optimized by 5-flod cross-validation (CV). Under the optimal input variables and model parameters, PLS models based on different input variables were constructed. The results show that compared with RAW-PLS and WT-PLS VIP-PLS can achieve better analysis performance, with the determination of the prediction set (k) of 0. 960 4 and root mean square error of prediction set (RMSEP) of 0. 034 1. Therefore, Raman spectroscopy combined with PLS is a fast and accurate method for analysing methanol content in methanol gasoline.