Determination of organochlorine pesticides in vegetable matrices by stir bar sorptive extraction with liquid desorption and large volume injection-gas chromatography-mass spectrometry towards compliance with European Union directives

A novel analytical approach to determine trace levels of 20 organochlorine pesticides (OCPs) in nine vegetable matrices (lettuce, spinach, green heart, green pepper, tomato, broccoli, potato, carrot and onion) is proposed, based on stir bar sorptive extraction followed by liquid desorption and large volume injection-gas chromatography coupled to mass spectrometry using the selected-ion monitoring mode acquisition (SBSE-LD/LVI-GC-MS(SIM)). The experimental procedure consists of a previous ultrasonic extraction of the freeze-dried vegetable samples (100.0 mg) with methanol (2 mL) followed by centrifugation and dissolution in aqueous media prior to SBSE-LD/LVI-GC-MS(SIM) under optimised conditions. Assays were performed on 30 mL aqueous samples using stir bars coated with 47 mu L of polydimethylsiloxane, an equilibrium time of 180 min (1000 rpm: 20 degrees C) and acetonitrile as back-extraction solvent, providing convenient analytical performance to monitor OCPs in vegetable matrices at the trace level. Besides the selectivity reached, the data obtained clearly demonstrate that the matrices involved have a strong effect on the recovery yields (10-110%) of the OCPs under study, in particular the green vegetables especially the leafy ones. By using the standard addition methodology, good linearity (r(2) > 0.99) and convenient precisions (RSD < 20%) were found for almost all cases, depending on the particular OCP and vegetable matrix involved. Furthermore enough sensitivity was also achieved (limit of detection < 10 mu g kg(-1)) for all OCPs under study towards compliance with the European Union regulations for the maximum residue limits of pesticides in agricultural vegetables. The methodology showed to be easy of work-up, fast, almost solventless with low sample amount requirement. when compared with conventional methods of sample preparation to screen pesticides in vegetable matrices. (C) 2009 Elsevier B.V. All rights reserved.