A Reusable Eu³⁺ Complex for Naked-Eye Discrimination of Methanol from Ethanol with a Ratiometric Fluorimetric Equilibrium in Methanol/Ethanol Mixtures

Immediate naked eye distinction of methanol from ethanol can be performed by simple dissolution, in each of these solvents, of either [Na][EuFOD₄] (1) complex or in mixture of products from the reaction between [P_6,6,6,14][Eu(FOD)₄] and NaOPhMe₃, referred as 2, ([P_6,6,6,14]⁺ = trihexyltetradecylphosphonium cation, FOD^– = 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dionate). Additionally, an easy, low-cost, efficient and fast spectrofluorimetric method for the detection and quantification of methanol in mixtures with ethanol is described. This method is based on the changes in the Eu³⁺ luminescence in the visible region due to the interaction of the [P_6,6,6,14][Eu(FOD)₄] complex with these alcohols. A limit of detection as low as 15 % (w/w) of methanol in mixtures of ethanol/methanol is discussed considering a linear calibration curve.