A simple method for methanol quantification in Spirits using UV Visible Spectroscopy and FTIR

Abstract

Although standards methods of food safety assessment are important, these methods are expensive and requires intensive work and time. Quality assessment for high alcohol in spirits is still a challenged for industries in developing states due to lack of financial support and technical assistance. Ultra violet visible spectroscopy (UV VIS) and Fourier Transform Infrared Spectroscopy (FTIR) offers the low cost alternative testing methods that are affordable with a short turnaround time for dissemination of results. In this work, methanol content in ethanol was assessed in two approaches using UV VIS and FTIR spectroscopy. For UV VIS method, Potassium dichromate was used as the chromogenic reagent. In FTIR, calibration curve was built by increasing methanol ration from 0 to 40% (m V-1) at the expense of ethanol while keeping deionised water (DO) constant at 5% (m V-1) concentration. This helps gauge the change in methanol concentration relative to ethanol. Results of analysis using UV VIS showed a strong negative correlation for Methanol concentration and absorbance value at UV region from 900 to 1100 cm-1 (r = 98.00, RMSE = 0.023) relative to increasing ethanol concentration. A strong peak was observed for methanol concentration at spectral region of 970 cm -1 which is related to the methanoic acid C-O bond. The FTIR spectra region at 900 to 1050 cm -1 was used for observing methanol concentration with absorbance. A strong correlation was established from spectral region of 1010 cm-1 to 1026 cm-1, enabling quantification of methanol (r= 0.99, RMSEC = 0.55). Methanol peak was observed at 1020 cm-1 region of the spectrum. A set of experimental repetition was made to determine limit of detection (LOD) for UV VIS and FTIR methods which was observed at 0.29 and 0.5 % (m V-1), respectively. The limit of quantification was 0.89 and 1.5 % (m V-1) for UV VIS and FTIR respectively. This study has reaffirmed the utilisation of UV VIS and FTIR as considerable alternative method for quality control of high alcohol in distilled spirits.