Alcohol analysis using a gold-coated unclad fiber sensor system

A sensor system using an optical fiber was developed and its response was tested to ethanol and ethylene glycol in water. The clad was removed from the fiber with sulfuric acid and its fiber core was coated with a gold film. The gold-coated unclad fiber responded rapidly and sensitively to the examined reagents, as compared to an unmodified unclad fiber. The calibration graph of transmittance vs. concentration showed a good relation in the range of 0 similar to 80% for ethanol and 0 similar to 40% for ethylene glycol. The detection limit was 0.5%. It was found that these alcohols could be determined in real time. The alcohol content in liquors (Shochu), which was determined directly by this method, showed 25.2 v/v%, very mean to the value (25 v/v%) indicated on the label of the Shochu bottle.