Study of menthol as a green extractant in dispersive liquid–liquid microextraction; application in extraction of phthalate esters from pharmaceutical products

A new mode of dispersive liquid–liquid microextraction performed in a narrow-bore glass tube has been developed for the extraction/preconcentration of some phthalate esters (EFs) in pharmaceutical samples. For the first time, menthol was used as the green extraction solvent in DLLME. Menthol (mg-level) was dissolved in a disperser solvent and injected into the aqueous sample solution placed in the tube (from the bottom side). Menthol fine droplets containing the extracted and preconcentrated analytes were collected on top of the tube in less than 5 min, and rapidly solidified by contact with air and formed a single solid piece. The solidified menthol was transferred into a vial with a conical bottom and dissolved in acetone (μL-level). Finally 1 μL of the solution was injected into gas chromatography-flame ionization detection for analysis of the extracted analytes. Five PEs e.g. di-methyl phthalate (DMF), di-ethyl phthalate (DEP), di-iso butyl phthalate (DIBP), di-n-butyl phthalate (DNBP), and di-iso octyl phthalate (DIOP) were selected as model analytes for evaluating the method. The influence of important parameters on the extraction efficiency were investigated in detail and optimized. Under the optimum experimental conditions, the method showed good linearities (R2 > 0.996), and broad linear ranges (10–10 000 μg L−1). Limits of detection were in the range of 1–8 μg L−1. The proposed method was applied on some pharmaceutical samples, and the obtained results were compared with those of some conventional methods, and revealed that this method has higher extraction efficiency. This technique is environmentally-friendly, affordable, efficient and convenient for sample preparation, with no need for centrifuging; making it fast and simple.