In-situ metathesis reaction combined with ultrasound-assisted ionic liquid dispersive liquid–liquid microextraction method for the determination of phenylurea pesticides in water samples

A novel microextraction technique, named in-situ metathesis reaction, combined with ultrasound-assisted ionic liquid dispersive liquid–liquid microextraction was developed for the determination of five phenylurea pesticides (i.e., diuron, diflubenzuron, teflubenzuron, flufenoxuron, and chlorfluazuron) in environmental water samples. In the developed method, 360 μL LiNTf2 aqueous solution (0.162 g/mL) was added to the sample solution containing a small amount of [C6MIM]Cl (0.034 g) to form a water-immiscible ionic liquid, [C6MIM]NTf2, as extraction solution. The mixed solutions were placed in an ultrasonic water bath at 150 W for 4 min and centrifuged at 3500 rpm for 10 min to achieve phase separation. After centrifugation, fine droplets of the extractant phase settled to the bottom of the centrifuge tube and were directly injected into the high-performance liquid chromatography system for analysis. The quantity of [C6MIM]Cl, the molar ratio of [C6MIM]Cl and LiNTf2, ionic strength, ultrasound time, and centrifugation time, were optimized using a Plackett–Burman design. Significant factors obtained were optimized by employing a central composite design. The optimized technique provides good repeatability (RSD 2.4 to 3.5%), linearity (0.5 μg/L to 500 μg/L), low LODs (0.06 μg/L to 0.08 μg/L) and great enrichment factor (244 to 268). The developed method can be applied in routine analysis for the determining of phenylurea pesticides in environmental samples.