Dual signaling of water contents of biofuel-relevant ethanol and butanol by pyranines

Abstract

Novel optical sensors for measuring the water contents of biofuel-relevant ethanol and 1-butanol based on the pyranine fluorophore were investigated. The diethylsulfonamide derivative of pyranine showed a pronounced absorption and fluorescent signaling in response to changes in the water content of ethanol and 1-butanol. This signaling was based on the increased dissociation of the acidic hydroxy group of pyranine in response to the increasing water content of the alcohol solutions. The signaling behavior of the sensors was readily analyzed by ratiometric measurements using the absorption and fluorescence characteristics of the undissociated and dissociated forms. Upon the derivatization to diethylsulfonamide, the signaling became more sensitive than that for its parent pyranine. The detection limits of the pyranine and diethylsulfonamide derivative for the measurement of the water content in ethanol were 1.9% and 0.03%, respectively. On the other hand, the detection limit of the diethylsulfonamide derivative for the determination of the water content in 1-butanol was 0.01%, whereas underivatized pyranine was not useful because of the limited solubility of the sensor. The practical application of this method for measuring the water content in ethanol and 1-butanol using a smartphone as an easy-to-use signal capturing device was also explored. (C) 2016 Elsevier B.V. All rights reserved.