An inquisitive fluorescence method for the real-time detection of trace moisture in polar aprotic solvents with the application of water rancidity in foodstuffs

Abstract

A simple analytical technique for detection of trace water in organic solvents is indispensable for moisture-free organic synthesis, environmental research, and food monitoring industry. Using a simple 4-methyl-2,6-diformyl phenol molecule (AH), we report the convenient fluorometric detection of trace water in various polar aprotic organic solvents having detection limits within 0.01–0.04% (v/v). Phenolate-oxygen of deprotonated AH (A⁻) forms an H-bond with a water molecule to exhibit a large spectral blue-shift from ∼485 to 440 nm in the UV-vis absorption or fluorescence excitation spectra, while unchanged emission characteristics were detected apparently due to dissociation of the H-bond in the excited state. The gradual blue-shift of the excitation band with the increase in water% (v/v) in the solution affects an opposite emission intensity changing behavior, from an increasing to a decreasing trend, due to the change in the excitation wavelength from 440 to 485 nm. Emission intensity changes of free A⁻ and A⁻/H₂O H-bonded species for each water addition are combined together for the spectral normalization to achieve water% induced a highly manifested linear emission response. The improved sensitivity allows us to quantify real-time atmospheric moisture incorporations in various polar aprotic solvents. The normalized emission intensity does not depend on AH concentration, and thus the water detection process is very effective for the estimation of water% in the solution with heterogeneous probe distributions. With this advantage, we succeed to estimate water% in various moisture-sensitive edible oils and dairy foods produced from water-rich raw materials. Therefore, the method can be applied to prevent water rancidity in foods with greater than its permissible limits via identifying higher moisture contamination.