Optimization of dispersive liquid–liquid microextraction for analysis of levonorgestrel in water samples using uniform design

Abstract

A simple, rapid and environment friendly extraction method, dispersive liquid–liquid microextraction (DLLME), was developed in combination with high performance liquid chromatography-diode array detector (HPLC-DAD) for the extraction and determination of levonorgestrel (LNG) in water samples. The main parameters affecting the microextraction efficiency were optimized for the first time using uniform design (UD). The statistical parameters of the derived model were R2 = 0.9898 and F = 85.608. The optimum conditions were 50 µL of trichloromethane (the extraction solvent), 50 µL of methanol (the disperser solvent), 0% (w/v) of sodium chloride and 140 s of the extraction time. Under the optimum conditions, a much lower volume of organic solvent was used, and the proposed method showed high enrichment factor (428), good linearity behavior (r = 0.9995) within a range of 1–300 µg L−1, low limit of detection (0.3 µg L−1), satisfactory repeatability (the relative standard deviation (RSD) of 5 µg L−1LNG was 5.9%, n = 6), and high recoveries (from 94.3 to 101.4%). The method was successfully applied for the determination of LNG in tap water, lake water and river water samples.