Journal of Chromatography A, 984 (2003) 245–252 www.elsevier.com / locate / chroma Application of single-drop microextraction and comparison with solid-phase microextraction and solid-phase extraction for the determination of a- and b-endosulfan in water samples by gas chromatography–electron-capture detection * ´ ´ M.C. Lopez-Blanco, S. Blanco-Cid, B. Cancho-Grande, J. Simal-Gandara Nutrition and Bromatology Group, Analytical and Food Chemistry Department, Faculty of Food Science and Technology, University of Vigo, Ourense Campus, E-32004 Ourense, Spain Received 12 September 2002; received in revised form 14 November 2002; accepted 14 November 2002 Abstract Water contamination due to the wide variety of pesticides used in agriculture practices is a global environmental pollution problem. The 98 / 83 European Directive requires the measurement of pesticides residues at a target concentration of 1.0 mg/l in surface water and 0.1 mg / l in drinking water. In order to reach the level of detection required, efficient extraction techniques are necessary. The application of a new extraction technique: single-drop microextraction (SDME), followed by gas chromatography with electron-capture detection, was assessed for determining a-endosulfan and b-endosulfan in water samples. Experimental parameters which control the performance of SDME, such as selection of microextraction solvent and internal standard, optimization of organic drop volume, effects of sample stirring, temperature and salt addition, and sorption time profiles were studied. Once SDME was optimized, analytical parameters such as linearity, precision, detection and quantitation limits, plus matrix effects were evaluated. The SDME method was compared with solid-phase microextraction and solid-phase extraction with the aim of selecting the most appropriate method for a certain application.  2002 Elsevier Science B.V. All rights reserved. Keywords: Single-drop microextraction; Extraction methods; Water analysis; Environmental analysis; Endosulfan; Pesticides 1. Introduction including tea, coffee, fruits and vegetables, as well as on cereals such as rice, maize, sorghum or other Endosulfan (mixture of a- and b-isomers) is an grains. insecticide and acaricide which acts as a poison to a Monitoring pesticide residues in waters is im- wide variety of insects and mites on contact. Al- portant for human health protection and environmen- though it may also be used as a wood preservative, it tal control. The European Union has set a maximum is used primarily on a wide variety of food crops, admissible concentration of 1.0 mg/l for each pes- ticide in surface water and 0.1 mg/l in drinking water [1]. *Corresponding author. Tel.: 134-988-387-000; fax: 134-988- Prior to chromatographic separation, pesticides are 387-001. ´ E-mail address: jsimal@uvigo.es (J. Simal-Gandara). extracted and preconcentrated from the aqueous 0021-9673 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0021-9673(02)01873-3