A rapid method for screening and determination test of methanol content in ethanol-based products using portable Raman spectroscopy

inspections, particularly on ethanol-based products. The influence of laser power density (PD) and exposure time (ET) on the Raman spectra similarity, specificity, selectivity, and accurate measurements for screening and determination of methanol content were carried out in this study. Raman spectra of samples were measured using a Raman handheld instrument. Measuring scales of PD and ET were varied from 50 to 300 milliWatt (mW) and 1000–5000 ms (ms), respectively. The similarity of Ramanspectra of those samples was statistically analysed with the help of hierarchical cluster analysis (HCA) and crosscorrelation function (Ccorrel). The subtracted Raman spectra and pure ethanol spectra were implemented to identify methanol content in samples of ethanol-based products specifically. The Raman spectra measured at PD of 200–300mW and clustered in one group by ward linkage method showed a similarity level of 99.98%. The variation of ET between 1000 and 5000 ms on fix PD of 300 mW showed high precision (RSD<2%) with more than 99% similarity of Raman spectra. Rinsing of PD was found to increase the signal: noise ratio, while prolonged exposure time reduced the signal: noise ratio. The precision and accuracy measurements were obtained by setting the PD and ET values of 300mW and 4000 ms, respectively. The subtracted Raman spectra with the spectra of absolute ethanol introduced a simultaneous screening of methanol containing alcohols and determination of both substances.