Development of chromogenic reactands for optical sensing of alcohols

A new class of chromogenic reactands (or 'chromoreactands') has been synthesised that reversibly interact with alcohols resulting in a change in absorbance. When embedded in plasticised PVC membranes, 4-(N,N-dioctylamino)-4'-trifluoroacetyiazobenzene (ETHT 4001) shows a significant signal change on exposure to aqueous ethanol solution with a decrease in absorbance at around 490 nm and an increase in absorbance at around 430 nn wavelength. The sensor layer exhibits a dynamic range from 2 to 50 vol% ethanol with highest sensitivity in the 5-35 vol% range. The limit of detection is 1.5 vol%. The absorbance of the sensor membrane is virtually insensitive to changes in pH, however, the magnitude of the relative signal change between plain buffer and buffer containing ethanol is pH dependent. A similar response is observed for 1-(N,N-dioctylamino)-4-(4-trifluoroacetylphenylazo)-naphthalene (ETHT 4002), however, with the absorbance shifted to longer wavelengths. The behaviour of the reactands dissolved in alcohols correlates with the selectivity of the dyes in the sensor membranes. (C) 1998 Elsevier Science S.A. All rights reserved.