Abstract
A fiber-optic sensor having a chitosan/poly(vinyl alcohol) blended membrane as the cladding and a Teflon protective coating was fabricated to determine ethanol in alcoholic beverages. The response was explained on the basis of an increase in the critical angle of the optical fiber by ethanol, which was induced by a shrinkage of the cladding membrane, leading to an increase in the refractive index. Crosslinking of the cladding membrane with glutaraldehyde enhanced the sensor sensitivity in the 0 - 70v/v% ethanol-content range. The Teflon coating removed interferences from sugars and organic acids commonly present in alcoholic beverages. The response time was within 2 min for 50v/v% ethanol and the relative standard deviation was within 1.7% in 20 repeated determinations during a 2-week period. A linear relationship was obtained between the response and the ethanol content in the 0 - 70v/v% range. The sensor was applied to the determination of ethanol in shochu, sake, wine, whiskey and beer and the results were consistent with the certified values and values obtained by the conventional specific-gravity method.
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