A rapid method for methanol quantification in spirits using UV - visible spectroscopy and FTIR

Shadrack, Ronick S. and Kotra, Krishna K. and Tari, Daniel and Tabi, Hancy and Botleng, Jacinta and Kelep, Rolina and Regenvanu, Ladyshia (2025) A rapid method for methanol quantification in spirits using UV - visible spectroscopy and FTIR. PeerJ Analytical Chemistry, 7 . NA. ISSN 2691-6630

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Abstract

Although standards methods of food safety assessment are important, these methods are relatively expensive and require intensive work and time. In alcohol beverage
industries, ultraviolet visible (UV-Vis) spectroscopy and Fourier transform infrared (FTIR) spectroscopy are reliable techniques for quality assessment of alcohol,
however, testing methods are often varying with calibration techniques and instrument specification. In this work, methanol content in ethanol was assessed in two approaches using UV-Vis with a developed calibration technique and FTIR
spectroscopy with a factory default scan function at every 2 nanometer (nm). For UV-Vis method, potassium dichromate was used as the chromogenic reagent, tested with methanol concentration ranging from 0.12% to 1% (mV−1). For FTIR method, spectra data was collected every 2 nm interval and calibration curve was built by increasing methanol ratio from 0% to 40% (mV−1) at the expense of ethanol while
keeping deionised (DO) water constant at 5% (mV−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 1,100 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 975 cm−1 which is related to the methanoic acid C-O bond. The FTIR spectra region at 900 to 1,050 cm−1 was used for
observing methanol concentration with absorbance. A strong correlation was established from spectral region of 1,010 to 1,026 cm−1, enabling quantification of methanol (r = 0.99, RMSEC = 0.55). Methanol peak was observed at 1,020 cm−1
region of the spectrum. A set of experimental repetition was made with methanol concentration of 0.02% to 0.5% and 0.1% to 5% for UV-Vis and FTIR, respectively, to determine the limit of detection (LOD) and limit of quantification (LOQ). The observation showed a 0.04% and 0.29% (mV−1) LOD for UV-Vis and FTIR method, respectively. The LOQ was 0.12% and 0.89% (mV−1) for UV-Vis and FTIR respectively. The integration of UV-Vis with potassium dichromate as chromogenic reagent and FTIR spectroscopy with comparatively 50% less data point still present a significant advancement in the test method for safety and quality control of alcohol
beverage products. These techniques not only enhance the ability to detect harmful substances but also provide a cost-effective and rapid alternative to traditional methods, making them invaluable tools for distilleries aiming to uphold high standards of quality.

Item Type:	Journal Article
Uncontrolled Keywords:	Methanol, Spirits, UV-visible spectroscopy, FTIR
Subjects:	Q Science > QD Chemistry
Divisions:	School of Agriculture, Geography, Environment, Ocean and Natural Sciences (SAGEONS)
Depositing User:	Krishna Kotra
Date Deposited:	29 Apr 2025 00:21
Last Modified:	29 Apr 2025 00:21
URI:	https://repository.usp.ac.fj/id/eprint/14930

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