Atrazine (2-chloro-4-ethylamino-6-isopropylamino-striazina), a herbicine from the family of s-triazine, widely used all over the world, has been detected in ground and surface waters in worrying levels of concentration. This compound has a low potential for bioaccumulation, moderate adsorption and mobility in soil. One way 1 Dra.; Fisica; Professora do Colegio Estadual do Parana; Endereco: Avenida Joao Gualberto, 250, Alto da Gloria, CEP: 80030-000, Curitiba, Parana, Brasil; E-mail: crisneiverth@yahoo.com.br Ambiencia Guarapuava (PR) v.11 n.2 p. 475 482 Jan./Abr. 2015 ISSN 1808 0251 Recebido para publicacao em 09/05/2012 e aceito em 16/10/2014 DOI:10.5935/ambiencia.2015.02.14nt Ambiencia Revista do Setor de Ciencias Agrarias e Ambientais V.11 N.2 Jan./Abr. 2015 476 is to determine atrazine is by Gas Chromatography coupled to Mass Spectrometry (CG-MS), using for the sample preparation the extraction in solid phase (SPE), which eliminates interferences and pre-concentrates the sample into a single step. This research aimed to develop a methodology for analysis of atrazine in water using Solid Phase Extraction in Gas Chromatography coupled with the Mass Spectrometry. The recovery was studied at two concentration levels (0.2 and 2.0 mg L-1), comparing the SIM and MS / MS. For quantification, the SIM method showed a better recovery (98% and 105%) and coefficient of variation (1.6%) at a concentration of 2.0 mg L-1. The detection limit of the SIM mode was 0.20 ng L-1 and the method was tested in surface water and leachate water of undisturbed soil columns of three headwaters. Only two samples of leachate water had concentrations of atrazine above those permitted by law (2.0 mg L-1).