Ion-Pair-Based Air-Assisted Liquid–Liquid Microextraction for the Extraction and Preconcentration of Phthalic Acids from Aqueous Samples

Abstract

In the present study, a rapid, simple, and highly efficient sample preparation method based on ion-pair air-assisted liquid–liquid microextraction using a low-density extraction solvent followed by high performance liquid chromatography–diode array detection has been developed for the extraction, preconcentration, and determination of three phthalic acids (phthalic acid, iso-phthalic acid, and terephthalic acid) in aqueous samples. In this method, a mixture of tri-butyl amine (as an ion-pair reagent) and toluene (as an extraction solvent) is transferred into an aqueous sample solution. Fine organic solvent droplets are formed by aspirating and dispersing of the mixture via syringe needle. After that, the formed ion-pairs are extracted into toluene, and after centrifuging, the obtained collected phase is transferred into a microtube and is evaporated to dryness under a stream of nitrogen at room temperature. The residue is re-dissolved in mobile phase and injected into the separation system for analysis. Under the optimum extraction conditions, the method showed low limits of detection and quantification between 0.09–0.24 and 0.29–0.78 ng mL−1, respectively. Extraction recoveries and enrichment factors were from 88 to 98 % and 443 to 491, respectively. Relative standard deviations for the extraction of 5 ng mL−1 of each analyte were less than 8.4 % for intra-day (n = 6) and inter-days (n = 5) precisions. Finally, different aqueous samples were successfully analyzed using the proposed method, and the target analytes were determined in some of them at ng mL−1 level.