Improving Fluorometric Determination of Water Content in Aprotic Solvents

Abstract

A fluorometric method allowing quantification of minute amounts of water in highly lipophilic solvents is proposed. This approach takes advantage of resonance energy transfer between 4-methylumbelliferone and Sudan I. The conditions required to observe effective energy transfer have been elucidated. The emission band of the donor molecule (4-methylumbelliferone) depends strongly on the water content-its position is affected by protolytic reactions occurring between the fluorescent dye and water in lipophilic solvent media. In consequence, the extent of overlap between the emission band of the donor and absorption peak of the acceptor scales with the water concentration. The sensitivity of this optical system can be considerably increased by addition of organic bases. The dependence of the emission band of 4-methylumbelliferone/Sudan I system on minute amount of water present in lipophilic solutions opens up possibility of determination of water content in these media at the unique wavelength, in a turn on mode. The presented system was successfully applied to determine water in model commercial oil samples. It was shown that using herein proposed method the increase of water contents in the sample can be observed as increase of the emission intensity, despite the native fluorescence of the vegetable oil samples. For these samples, a good correlation with golden standard Karl Fischer titration was obtained.