FIBEROPTIC SENSOR WITH A CHITOSAN POLY(VINYL ALCOHOL) CLADDING FOR THE DETERMINATION OF ETHANOL IN ALCOHOLIC BEVERAGES

A fiber-optic sensor having a chitosan/poly(vinyl alcohol) blended mem brane as the cladding and a Teflon protective coating was fabricated t o determine ethanol in alcoholic beverages. The response was explained on the basis of an increase in the critical angle of the optical fibe r by ethanol, which was induced by a shrinkage of the cladding membran e, 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 i nterferences from sugars and organic acids commonly present in alcohol ic beverages. The response time was within 2 min for 50v/v% ethanol an d the relative standard deviation was with in 1.7% in 20 repeated dete rminations 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 cert ified values and values obtained by the conventional specific-gravity method.