Optical alcohol sensor using lipophilic Reichardt's dyes in polymer membranes

Two lipophilic derivatives of Reichardt's phenolbetaine were dissolved in t hin layers of plasticized poly(ethylene vinyl acetate) copolymer. These lay ers were coated with microporous white PTFE in order to allow reflectance ( transflectance) measurements to be performed. The sensor layers respond to aqueous ethanol with a colour change from green to blue when increasing the ethanol content. The highest signal changes are observed at a wavelength o f 750 nm with a linear calibration function up to 20% v/v ethanol and a det ection limit of 0.1% v/v. The layers also exhibit strong sensitivity to ace tic acid which affects real measurements of beverages. However, this limita tion can be overcome by adjusting the basic pH of the sample solution. The correlation of ethanol content measured by enzymatic tests or gas chromatog raphy correlates well with the data obtained using the ethanol sensor descr ibed here. (C) 2001 Elsevier Science B.V. All tights reserved.