Determination of 81 multiclass pesticides in fresh foodstuffs by a single injection analysis using gas chromatography-chemical ionization and electron ionization tandem mass spectrometry

A new analytical method has been proposed to determine 81 multiclass pesticide residues in vegetables. It is based on a fast extraction of the pesticides with dichloromethane and a further analysis of the extract by gas chromatography-tandem mass spectrometry (GC-MS-MS). For that, a single injection of the extract is carried out using the optimum ionization mode (electron ionization (EI) or chemical ionization (CI)) for each pesticide. The presented method reduces the total time of analysis with respect to those which propose two different injections in order to analyze such number of pesticides, being more suitable for its usage in routine laboratories. The method was validated in order to be applied to real samples. Recoveries in cucumber at two different fortification levels were evaluated and ranged between 73% and 108% for all pesticides. The relative standard deviation (R.S.D.%) was lower than 22% in all cases. The calculated limits of detection (LOD) and quantification (LOQ) were lower than the maximum residue levels established by European legislations. Inter-day recoveries and precision were evaluated too. The method has been successfully applied to the analysis of approximately 4000 real samples from El Ejido (Almerfa, Spain). (C) 2003 Elsevier Science B.V All rights reserved.