Monitoring pesticide residues in greenhouse tomato by combining acetonitrile-based extraction with dispersive liquid–liquid microextraction followed by gas-chromatography–mass spectrometry Armindo Melo a , Sara C. Cunha a , Catarina Mansilha b,e , Ana Aguiar c , Olívia Pinho a,d , Isabel M.P.L.V.O. Ferreira a,⇑ a REQUIMTE, Departamento de Ciências Químicas, Laboratório de Bromatologia e Hidrologia da Faculdade de Farmácia da Universidade do Porto, Portugal b Instituto Nacional de Saúde Dr. Ricardo Jorge, Portugal c REQUIMTE, Faculdade de Ciências da Universidade do Porto, Portugal d Faculdade de Ciências da Nutrição e Alimentação da Universidade do Porto, Portugal e REQUIMTE, Universidade do Porto, Portugal article info Article history: Received 7 February 2012 Received in revised form 1 May 2012 Accepted 28 May 2012 Available online 7 June 2012 Keywords: Tomato Pesticides Improved extraction procedure Dispersive liquid–liquid microextraction Gas chromatography–mass detection abstract A multiclass and multiresidue method for pesticide analysis in tomato was validated. Extraction and pre- concentration of the pesticide residues from acetonitrile extracts was performed by using dispersive liquid–liquid microextraction (DLLME) technique, followed by gas chromatography–mass detection. DLLME was performed using carbon tetrachloride as extractive solvent and acetonitrile extract as disper- sive solvent, in order to increase enrichment factor of the extraction procedure. Validation parameters indicated the suitability of the method for routine analyses of thirty pesticides in a large number of sam- ples. In general, pesticide recoveries ranged between 70% and 110% and repeatability ranged between 1% and 20%. The proposed method was applied to the monitoring of pesticides in tomatoes grown during winter in greenhouses. Among the compounds considered in this work, cyprodinil was found in tomato at concentrations of 0.33 mg/kg, other pesticides like azoxystrobin, fenhexanid, tolyfluanid, k-cyhalothrin and trifloxystrobin were also detected, but, not quantified. Ó 2012 Published by Elsevier Ltd. 1. Introduction Tomatoes (Lycopersicum esculentum sin.: Solanum lycopersicum, Lycopersicum lycopersicum) belong to the Solanaceae family and correspond to one of the most widely grown vegetables in the world (Engindeniz, 2006). This fruit vegetable is typically produced in spring–summer season, however, in south Europe it is produced during all year in greenhouses (Bidari, Ganjali, Norouzi, Hosseini, & Assadi, 2011). Thus, consumers can eat fresh tomato even during winter. Usually it is consumed in salad dishes without any cooking treatment. Commercial greenhouses are widely utilized to produce pre- mium-quality fruits and vegetables by providing optimal growth conditions for these plants (Acquaah, 2002). Moderate temperature and high humidity promote plant development but also contrib- utes to pests and diseases spread. Moreover, in greenhouses the cultures follow up each other in a non-stop rotation by the virtu- ally year-round culture of crops, allowing the survival of pests and diseases. Indeed, greenhouse requirements for best tomato production are also favorable for development of fungal diseases, such as late blight (Phytophtora infestans) and gray mold (Botrytis cinerea)(Angioni, Porcu, & Dedola, 2011). Also, insects and mites are ever-present in greenhouses and so, insecticides are widely used in tomato protection programs (Nelson, 1998). For this rea- son, integrated pest management strategies require spraying with different types of fungicides and insecticides (Acquaah, 2002; Bidari et al., 2011). Consequently, monitoring of pesticide residues in greenhouse tomatoes has become essential to ensure food safety and prevent bioaccumulation of pesticide residues through the food chain. Concentrations of pesticides in food commodities such as tomato are normally low. Thus, pretreatment/extraction procedures are re- quired in order to isolate the analytes from the complex tomato ma- trix, remove interfering compounds and achieve a sufficient sensitivity to guarantee that the detection limits of the method are in agreement with EU legislation requirements, established by max- imum residue levels (MRLs) (Regulation (EC) No. 396/2005, 2005). Gas chromatography coupled to mass detection is widely used in the analysis of pesticides that are highly volatile (Likas, Tsiropoulos, & Miliadis, 2007), whereas liquid chromatography is preferred in the analysis pesticides with low volatility (Sannino & Bandini, 2005). 0308-8146/$ - see front matter Ó 2012 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.foodchem.2012.05.112 ⇑ Corresponding author. E-mail address: isabel.ferreira@ff.up.pt (I.M.P.L.V.O. Ferreira). Food Chemistry 135 (2012) 1071–1077 Contents lists available at SciVerse ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem