The water content of organic solvents was determined by the ligand dissociation of a tris(2-methyl-8-quinolinolato)indium(III) complex. Water in the organic solvent reacts with the indium complex to induce a ligand-exchange reaction. The fluorescence of deprotonated 2-methyl-8-quinolinol disappears when the ligand-exchange reaction forms a neutral molecule; thus, the complex can serve as a turn-off water-detection sensor. We measured the water content of various organic solvents, including ethyl acetate, 1-octanol, and ethanol. The indium complex was dissolved in a water-containing organic solvent, the fluorescence of the 8-quinolonolate ion was measured, and determination curves were constructed based on the decrease in fluorescence intensity. To demonstrate the versatility of the present method, we measured the water content of alcoholic drinks. These results are consistent with the data obtained by Karl Fischer (KF) titration. Although the limits of detection and quantification were not as low as those of the KF titration, the simple experimental setup and procedure of this method are favorable for its application.
Watanabe et al. (Mon,) studied this question.