Liquid phase microextraction based on the solidification of a floating ionic liquid combined with high-performance liquid chromatography for the preconcentration of phthalate esters in environmental waters and in bottled beverages

Abstract

A novel liquid phase microextraction method based on the solidification of floated ionic liquids (SFIL-LPME) was developed to determine four phthalate esters (diethyl phthalate, diallyl phthalate, benzyl butyl phthalate, and dicyclohexyl phthalate) in environmental waters and bottle beverages and subsequently separate them using high-performance liquid chromatography. In this work, we customized a tributyldodecylphosphonium tetrafluoroborate ([P_{4 4 4 12}][BF₄]) ionic liquid (IL) to obtain a low density such that it can be solidified at a low temperature, and then used as an extraction solvent in liquid-phase microextraction based on the solidification of floated organic drops (SFO-LPME). This means that more potential ILs can be customized to broaden extraction solvents in SFO-LPME. To identify the significant factors that affect extraction efficiency, parameters such as the volume of [P_{4 4 4 12}][BF₄], the extraction time, the rotation speed, the extraction temperature and the ionic strength were optimized using a Plackett–Burman design. A central composite design was then used to optimize the identified significant factors to study the effect of interactions on the experiment. Under these optimized conditions, the extraction recoveries of the four phthalate esters in water samples ranged from 73.0 to 94.6% and in bottled beverage were from 70.2 to 101.3%, with relative standard deviations (RSDs) ranging from 0.6 to 8.2% and 0.6 to 7.8%. Good linearity for both water samples and bottled beverages were obtained in the range of 5–500 μg L⁻¹, with correlation coefficients greater than 0.9993. The limits of detection for the four phthalate esters varied from 0.27 to 1.1 μg L⁻¹ for water samples and 1.22 to 2.36 μg L⁻¹ for bottled beverages. The two developed methods were then successfully applied to the determination of phthalate esters in environmental waters and bottled beverages.