Improved liquid–liquid–liquid microextraction method and its application to analysis of four phenolic compounds in water samples

An improved liquid–liquid–liquid microextraction (LLLME) technique has been put forward based on the principle of single drop LLLME. In the technique, a vial insert was firstly utilized as acceptor phase container. Because the diameter of the bottom of the vial insert was small, the contact area between the acceptor phase and the vial insert was bigger than that between microsyringe and microdrop of acceptor phase in single drop LLLME, and the stability of microdrop was increased markedly. More acceptor phase could be held in the improved method than that in single drop LLLME, and the sensitivity of the method was increased. The sample vial and vial insert were horizontally placed so that the density of organic solvent has little effect on the selection of organic solvents. Aqueous ammonia and toluene were selected as the acceptor phase and the organic phase, respectively. The improved method was successfully applied to determine four phenolic compounds in real aqueous samples. Good recoveries that ranged from 82.2% to 117.2% were obtained. The intra-day and inter-day reproducibilities (RSD) were under 4.8% and 6.8%, respectively. The extraction efficiency of the improved method was 11–47 times higher than that of single drop LLLME method. The improved LLLME method is economical, rapid, simple, efficient, low organic solvent consumption and no cross-containment. This method is very suitable for the extraction of ionizable and chargeable analyte in complex environmental or biological samples.