Three-phase liquid-phase microextraction for the determination of partition coefficient and analysis of nitrophenols

Abstract

Liquid-phase microextraction (LPME) has become a very popular technique because it is inexpensive, easy to operate and solvent-free. As the distinct advantages of LPME were proven, it is therefore of interest to investigate the three-phase liquid-phase LPME and the partition coefficient of selected nitrophenols. In this study, a three-phase hollow fiber liquid-phase microextraction (HF-LPME) method coupled with capillary electrophoresis (CE) has been developed. The selected nitrophenols were extracted from 14 mL aqueous solution (donor solution) with the pH adjusted to pH 3 into an organic phase (1-octanol) immobilized in the pores of the hollow fiber and finally back-extracted into 40.0 µL of the acceptor phase (NaOH) at pH 12.0 located inside the lumen of the hollow fiber. The extractions were carried out under optimum conditions (donor solution: 0.05 M H3PO4, pH 3.0; organic solvent: 1-octanol; acceptor solution: 40 µL of 0.1 M NaOH, pH 12.0; agitation rate: 1050 rpm; extraction time: 15 min). Under optimized conditions, the limit of detection (LOD) obtained were between of 0.01 – 0.04 ppm. Excellent enrichment factors of up to 398-folds were obtained. The determination of partition coefficients of analytes in three-phase HF-LPME was successfully achieved. It was found that the partition coefficient (Ka/d) values were high for 2-nitrophenol, 3-nitrophenol, 4-nitrophenols, 2,4- dinitrophenol and 2,6-dinitrophenol and the individual partition coefficients (Korg/d and Ka/org) promoted efficient simultaneous extraction from the donor through the organic phase and further into the acceptor phase. The developed method was successfully applied for the determination of nitrophenols in water samples.