Novel Method for Identification and Quantification of Methanol and Ethanol in Alcoholic Beverages by Gas Chromatography-Fourier Transform Infrared Spectroscopy and Horizontal Attenuated Total ReflectanceFourier Transform Infrared Spectroscopy

Abstract

Numerous methods are being used to identify and quantify methanol and ethanol in alcoholic beverages, including country liquors. Some of the known methods are density and refractive index measurements, and spectrophotometric measurements using Schiff's reagent or chromatropic acid. Other advanced techniques involve head space gas chromatography (GC), GCflame ionization detection, high-performance liquid chromatography, enzymatic reactions, and biosensors. However, identification and quantification of methanol and ethanol in beverages can be accurately done using GC-Fourier transform infrared spectroscopy (FTIR) and horizontal attenuated total reflectance (HATR)-FTIR. Identification of alcohols is possible from library matching of the IR spectra obtained from GC-FTIR. In water, methanol and ethanol show a very strong peak for CO, stretching at 1015.3 and 1044.2 cm1, respectively. The strong absorption of vibrational stretching frequency of CO present in alcohols was used for quantification purposes. The absorptions of CO group frequency of alcohols in water mixtures were measured using HATR-FTIR with a zincselenide crystal. Samples were placed directly on the HATR crystal, with alcohol concentrations ranging from 0.2 to 50.0 (v/v). The plot of absorptions against concentrations of methanol and ethanol obeyed Beer's law (r2 0.9998 and 0.9987, respectively), from which alcohol in the mixtures was quantified. Propan-2-ol and n-butanol showed no interference. The method is validated from absorption measurements of known mixtures of standard ethanol in water. This is a simple, specific, rapid, accurate, and nondestructive method of identification and quantification of methanol and ethanol in mixtures. It can be used to ascertain methanol contamination in alcoholic beverages that can lead to death or methanol poisoning by alcohol consumption.

Quantification of adulterants in mezcal by means of FT-MIR and FT-NIR spectroscopy coupled to multivariate analysis

“…The optimal conditions to obtain the MIR spectra were: 4 cm −1 resolution and the number of scans for each spectrum was adjusted to 64. These conditions coincide with other authors (Ozturk et al, 2012;Sharma et al, 2009). The optimal conditions to obtain the NIR spectra were: 4 cm −1 spectral resolution and 32 co-added scans, the above coincides with Yang et al (2016).…”

Twisted-Planar-Twisted expanded porphyrinoid dimer as a rudimentary reaction-based methanol indicator

“…It is used as a denaturant in laboratory and industrial-grade ethanol but can also be present in distilled beverages whose quality is not carefully controlled 30 , 31 . Not surprisingly, therefore, considerable effort has been devoted to the problem of sensing methanol in the presence of ethanol and other potentially competing analytes 32 , 33 . Currently, physical techniques, such as gas chromatography 34 , Fourier transform infrared spectroscopy 35 , and Raman spectroscopy 36 , define the gold standard for methanol sensing.…”

Pattern Recognition Approach for the Screening of Potential Adulteration of Traditional and Bourbon Barrel-Aged Maple Syrups by Spectral Fingerprinting and Classical Methods

“…The fingerprint region of 800–1200 and 800–1000 cm −1 was used to discriminate BBL and traditional maple syrups using FT-IR and Raman spectrometers, respectively. For the FT-IR system, most of the model variance was explained by intensity differences of bands located at 878 cm −1 , which is closely related to the symmetric stretching of the primary alcohol group, and 1034 cm −1 , which is related to the C-O bond stretching [ 42 , 43 ]. For the Raman system, most of the model variance was explained by the band at 879 cm −1 , which was also related to the alcohol group’s concentration [ 44 ].…”