Natural Eutectic Solvent-Based Temperature-Controlled Liquid–Liquid Microextraction and Nano-Liquid Chromatography for the Analysis of Herbal Aqueous Samples

In this work, two novel (-)-menthol-based hydrophobic natural eutectic solvents with vanillin and cinnamic acid were prepared and applied as extraction solvents. In this regard, 12 endocrine disruptors, including phenol, 2,4-dimethylphenol, 2,3,6-trimethylphenol, 4-<i>tert</i>-butylphenol, 4-<i>sec</i>-butylphenol, 4-<i>tert</i>-amylphenol, 4-<i>n</i>-hexylphenol, 4-<i>tert</i>-octylphenol, 4-<i>n</i>-heptylphenol, 4-<i>n</i>-octylphenol, and 4-<i>n</i>-nonylphenol and bisphenol A, were studied in a green tea drink. A temperature-controlled liquid-liquid microextraction was used as the extraction method, and nano-liquid chromatography-ultraviolet detection was used as the separation and determination system. Different parameters affecting the compatibility of the non-ionic eutectic solvents with water-polar organic solvent mixtures and chromatographic and detection systems were optimized, including injection/dilution solvent, injection mode, mobile phase composition, and step gradient. With the same purpose, two stationary phases were tested, including XBridge^® C₁₈ and a mixed-phase Cogent C₃₀-XBridge^® C₁₈. Finally, the greenness and blueness of the methodology were assessed to evaluate the environmental profile and usability of the procedure.