Ultrasensitive 4-methylumbelliferone fluorimetric determination of water contents in aprotic solvents

•4-Methylumbelliferone in aprotic solvents shows linear dependence of fluorescence intensity increase on water contents.•For low water contents, higher sensitivity is offered compared to Karl Fischer titration.•Organic compounds of protolitic character increase the sensitivity of determination.•Strong acid or base has similar effect on the system as introduction of pure water.

A novel approach to the quantification of relatively small amounts of water present in low polarity, aprotic solvents is proposed. This method takes advantage of protolitic reaction of 4-methylumbelliferone dissolved in the solvent with water, acting as a base. The low emission intensity neutral 4-methylumbelliferone is transformed in reaction with water to a highly fluorescent anionic form. Thus the increase in emission intensity is observed for increasing water contents in aprotic solvents. For low water contents and highly lipophilic solvents, this method yields (in practical conditions) higher sensitivity compared to biamperometric Karl Fischer titration method in volumetric mode.It is also shown that organic compounds of protolitic character (amines, acids) not only interfere with water contents determination but increase the sensitivity of emission vs. water contents dependence. Introduction of aqueous solution of strong acid or base (HCl or NaOH) has similar effect on the system as introduction of pure water.

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