Response Surface Modeling of Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction for Determination of Benzene, Toluene and Xylenes in Water Samples: Box–Behnken Design

A simple, fast and effective pre-concentration procedure for the extraction of benzene, toluene and xylenes isomers (BTX) was developed using an ultrasound-assisted dispersive liquid–liquid microextraction coupled with gas chromatography-flame ionization detector in water samples. The effects of different experimental parameters in the extraction step including type and volume of extraction and dispersive solvents, ionic strength, extraction time and sample volume were studied using two techniques, namely one-variable-at-a-time and response surface methodology. The results of “one-variable-at-a-time” showed that the ionic strength and extraction time were not significant on the extraction efficiency. Therefore, a three-factor, three-level Box–Behnken experimental design was employed to optimize the BTX extraction. The optimal conditions were determined to be a volume of extraction solvent (chloroform) of 51 μL, volume of dispersive solvent (methanol) of 514 μL and volume of sample of 12 mL. The enrichment factors of 241.2–305.1, the limit of detections of 205–382 ng L−1 were obtained for the BTX at the optimum conditions. In addition, the relative standard deviations for 50 μg L−1 of the BTX in the water samples were found to be in the range of 1.9 %–5.7 % (n = 5). The developed procedure was then applied for the extraction and determination of BTX in the water samples.