Development of a Green Alternative Vortex-Assisted Dispersive Liquid–Liquid Microextraction Based on Natural Hydrophobic Deep Eutectic Solvents for the Analysis of Phthalate Esters in Soft Drinks

A new green alternative vortex-assisted dispersive liquid–liquid microextraction method based on a natural hydrophobic deep eutectic solvent was developed for the extraction of 14 phthalic acid esters and one adipate in cold infusions and tonic waters. Analyses were carried out using ultra-performance liquid chromatography coupled to tandem mass spectrometry. Different eutectic mixtures based on the monoterpene thymol (essential oil of thyme) and medium-chain fatty acids (octanoic and decanoic acids) at different molar ratios were tested in this regard. The effect of different factors affecting extraction efficiency was optimized through a systematic approach. The method was validated by means of precision, matrix-matched calibration, recovery, and repeatability studies using two different deuterated surrogate standards (dibutyl phthalate-3,4,5,6-d₄ and dihexyl phthalate-3,4,5,6-d₄). The method proved to be linear (determination coefficients were higher than 0.9912) with normalized recoveries in the range between 71 and 124% (except for di-n-octyl phthalate at a low concentration level in tonic water [63%]). Then, the method was applied for the analysis of the selected compounds in 3 pineapple/green tea-based cold infusions and 8 tonic beverages. Finally, the greenness of the procedure was assessed using the Analytical Eco-Scale. This paper represents the first application of this natural hydrophobic deep eutectic solvent for the analysis of phthalate esters, and, also the first time, these compounds are analyzed in cold infusion and tonic water.