Dispersive liquid—liquid microextraction for the determination of three cytokinin compounds in fruits and vegetables by liquid chromatography with time-of-flight mass spectrometry

The paper presents a novel approach for the determination of three cytokinin compounds, thidiazuron (TDZ), 1,3-diphenylurea (1,3-DPU) and forchlorfenuron (CPPU), in fruit and vegetables samples using liquid chromatography with electrospray ionization and time-of-flight mass spectrometry (LC—ESI—TOFMS). Analytes were extracted from the sample matrix with ethanol, and the extract, after dilution with water, was submitted to dispersive liquid—liquid microextraction (DLLME). Once acetonitrile and 1,2-dichloroethane had been selected as extraction and disperser solvents, respectively, the influence of the following experimental parameters was studied using a Plackett—Burman design: volume of extraction and disperser solvents, sample mass and time and speed of centrifugation. The best analytical conditions were 250 µL 1,2-dichloroethane, 1.5 mL acetonitrile, 5 g sample mass, and centrifugation at 3000 rpm for 3 min. The optimized method provided DLs in the range 0.02—0.05 ng g−1, depending on the compound. Satisfactory recovery values between 89 and 106% were obtained for spiked samples (kiwifruit, watermelon, grape and tomato) in the 0.2—1.0 ng g−1 concentration range, depending on the compound. None of the target analytes was detected in any of the samples analyzed.