Low concentration natural methanol exists in most alcoholic beverages and usually causes no immediate health threat. Nevertheless,
it is possible to have natural occurring methanol in beverages with concentration as high as 18 g/L of ethanol; or equivalent
to 0.72% methanol in 40% ethanol, in alcohol (1). Current EU regulation limits naturally occurring methanol to below 10 g/L
of ethanol; or equivalent to 0.4% methanol in 40% ethanol.
Raman spectroscopy has been shown to be an effective tool in compositions analysis as well as adulteration identifications
in foods (2). In the alcoholic beverage industry, the standard composition analysis method were more expensive and time-consuming
gas chromatography (3). Here, we present a Raman spectroscopy method for a quick and lower cost alternative to verify the
existence of low concentration methanol in alcohol.
40% ethanol/water solution was prepared using 200-proof ethanol and distilled water. HPLC grade methanol was added into the
40% ethanol solution to make samples with methanol concentration ranging from 50 ppm to 2.5%. An Enwave Optronics' ProRaman
instrument with laser excitation at 785 nm was used for the measurements. The sample solutions were measured in quartz cuvette
in a sample holder. Figure 1 depicts the results of the measured spectra in the fingerprint region of the Raman spectra.
Figure 1: The fingerprint range spectra of the various solutions.