Solvatochromogenic flavone dyes for the detection of water in acetone

Two flavone dyes, 3-hydroxy-4'-N,N-dimethylaminoflavone (HMAF) and 4'-N,N-d imethylaminoflavone-3-yl methacrylate (DMAFMA), have been investigated as s olvatochromogenic fluorophores for the determination of water in acetone. T he solvent-dependent absorption and fluorescence spectral characteristics o f HMAF and DMAFMA have been studied in a series of organic solvents and wat er/acetone binary mixtures. Spectral shifts of the compounds were observed in these solvents and their mixtures. DMAFMA exhibits a normal fluorescence emission in various solvents. Besides the normal emission, HMAF shows an a bnormal band which is attributed to intramolecular proton transfer occurrin g across a pre-existing intramolecular hydrogen bond. As a result of the pr oximity effect, conformation change, and the formation of intra- or intermo lecular hydrogen bonds, the emission intensity changes with the change in s olvents polarity. A maximum change was observed for HMAF in ethanol, and fo r DMAFMA in tetrahydrofuran. With incremental addition of small amounts of water to HMAF and DMAFMA acetone solution, spectral red shifts of the compo unds were also observed, while the changes in the fluorescence intensity we re in a reverse direction for these two compounds. Owing to the formation o f solvate complexes involving hydrogen bonding with the increase of water c ontent, the fluorescence intensity of HMAF increases and that of DMAFMA dec reases. HMAF fluorescence emission intensity changes as a function of water content in the 0.0-10.0% range, with a detection limit of 0.02%. By using the DMAFMA reagent, a linear range of 0.0-3.0% and a detection limit of 0.0 05% are achieved. Small amounts of alcohols and aldehydes show no substanti al effect on the determination of water in acetone samples with the flavone dyes. The proposed methods were applied to the determination of water in r eagent-grade acetone. The results agree well with those obtained by the gas chromatographic method. (C) 1999 Published by Elsevier Science B.V. All ri ghts reserved.