Natural products as probes for the spectral analysis and sensitive detection of metal-containing ionic liquids.

A new analytical method was developed for the rapid detection of metal-containing ionic liquids (MCILs) using the natural products (NPs) as fluorescent probes. Based on electrostatic potential (ESP) distribution and conductor-like screening model for real solvents (COSMO-RS) simulation, the possible interactions between quercetin, emodin, curcumin, esculetin and 1-butyl-3-methylimidazole tetrachloroferrate ([Bmim][FeCl4]) were predicted, and the ultraviolet response, concentration titration experiments and fluorescence response of NPs and [Bmim][FeCl4] were studied. Both theoretical and experimental studies indicated that esculetin showed the best corresponding performance to [Bmim][FeCl4] and then was selected as fluorescent probe molecule for the detection of a series of similar ionic liquids containing Zn2+, Cu2+ and Al3+. The linear range of this analytical method towards [Bmim][FeCl4] was 5 ∼ 30 μM (R2 = 0.9957) with the relative standard deviation of 2.1 % and the limit of detection (LOD) of 1.08 μM. Recoveries, measured in the standard ethanol solution with the added concentration of 5 μM, were determined as 98.1 ∼ 102.5 % by the standard addition method. According to all the studied results, the probe of natural product possessed good selectivity, repeatability, and stability, which could be fixed onto filter paper to detect [Bmim][FeCl4] in more intuitive way.