pubs.acs.org/JAFC Published on Web 02/08/2010 © 2010 American Chemical Society 2818 J. Agric. Food Chem. 2010, 58, 2818–2823 DOI:10.1021/jf904465s Analysis of Forchlorfenuron in Vegetables by LC/TOF-MS after Extraction with the Buffered QuEChERS Method ANTONIO VALVERDE,* ,† ANA AGUILERA, † CARMEN FERRER, † FRANCISCO CAMACHO, ‡ AND ANITA CAMMARANO § † Pesticide Residue Research Group, Faculty of Experimental Sciences, and ‡ Vegetal Production Department, Faculty of Agronomy, University of Almeria, 04071-Almerı´a, Spain, and § Istituto di Chimica Agraria ed Ambientale, Universit a Cattolica del Sacro Cuore, Piacenza, Italy This paper describes the application of liquid chromatography time-of-flight mass spectrometry (LC/TOF-MS), with electrospray ionization, for residue analysis of forchlorfenuron in tomato, zucchini and watermelon. The assessed method includes a sample preparation step based on the buffered QuEChERS approach. The TOF-MS fragmentation pattern of forchlorfenuron was studied at different fragmention voltages in the range of 120-270 V. Analyses were carried out under full-scan conditions by using the extracted ion chromatogram (XIC) of the m/z 248 ion with a 0.2 Da window. The linearity of the analytical response across the studied range of concentrations (10-500 μg/kg) was excellent, obtaining correlation coefficients higher than 0.999, and relative standard deviations of the response factors lower than 14%, for the 15 linear calibration curves of forchlorfenuron evaluated along the complete validation study. No significant matrix effects were observed. The signal-to-noise ratios obtained for the 10 μg/kg forchlorfenuron in matrix matched standards were >70 for all three matrices. Recovery studies were carried out on spiked tomato, zucchini and watermelon blank samples, at three concentration levels (10, 50, and 200 μg/kg) performing five replicates at each level. Forchlorfenuron mean recoveries ranged between 80% and 87% in watermelon and zucchini, and between 65% and 71% in tomato, obtaining in all cases relative standard deviation values lower than 10%. The method readily achieved a lowest validated level of 10 μg/kg, which was fit-for-purpose in residue monitoring applications. KEYWORDS: Analysis; forchlorfenuron; LC/TOF-MS; QuEChERS; fruits and vegetables INTRODUCTION Plant growth regulators, such as auxins, gibberellins and cyto- kinins, are used to improve fruit set and development in many crops, overall when the pollination and fertilization conditions are unfavorable ( 1 ). Forchlorfenuron, 1-(2-chloro-4-pyridyl)-3- phenylurea, is a relatively new plant growth regulator belonging to the synthetic cytokinins group ( 2 ), extensively used in recent years for increasing fruit size in many crops, particularly in grapes and kiwifruit ( 3 , 4 ). It is also very effective to induce artificially parthenocarpy (the development of the ovary into fruit without fertilization or seed formation), being an alternative to natural pollination in some crops, such as melon, watermelon and pump- kin ( 5 , 6 ). During the present decade, forchlorfenuron has been registered in many countries and, according to the USDA database for Maximun Residue Limits (MRLs), the tolerances established for its residues around the world range between 10 μg/kg and 100 μg/kg, depending on crop and country. Particular examples of forchlorfenuron MRLs for kiwifruit are 10 μg/kg in Australia, 40 μg/kg in USA, 50 μg/kg in EU, or 100 μg/kg in Japan ( 7 ). By now, only a few papers have been published on the analysis of forchlorfenuron residues in agricultural products. Hu and Li reported the determination of forchlorfenuron residues in water- melon by solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) ( 8 ), Sharma and Awasthi studied the behavior of forchlorfenuron residues in grape by using liquid chromatography with UV detector as analytical technique ( 9 ), and Valverde et al. used liquid chromatography with tandem mass spectrometry (LC/MS-MS) to evaluate the persistence of forchlorfenuron residues in watermelon after applying an indivi- dual spray treatment to the flower ovary at the anthesis stage ( 10 ). Finally, in 2008, Suarez-Pantaleon et al. described the develop- ment of immunoassays for the detection of forchlorfenuron ( 11 ), but this technology has not been yet validated for the analysis of its residues in vegetables. Liquid chromatography with time-of-flight mass spectrometry (LC/TOF-MS) has been recently demonstrated to be a sensitive and selective technique for the determination and identification/ confirmation of pesticide residues in fruits and vegetables, show- ing a great potential to be used in routine multiresidue analysis ( 12 -15 ). However, the use of LC/TOF-MS for the identification and quantitation of forchlorfenuron in vegetables has not been yet reported. The objective of this work was to develop and evaluate a rapid method for determining forchlorfe- nuron residues in vegetables by using LC/TOF-MS and the quick, *Corresponding author. E-mail: avalverd@ual.es. Fax: þ34 950015008.