The atrazine is used in control in pre and post-emergence weeds of broad leaved in plantations of sugar cane, corn, orange. The contamination of water resources by atrazine can have serious consequences for the environment and for human health. In this context, this work proposes a method of concentration of atrazine surface water based on aqueous two-phase system (ATPS) composed of tetrahydrofuran (THF) and glycerol. The tie-lines were determined, and subsequently recovery of the atrazine in THF- rich phase was optimized from 70.90 to 96.47 wt%. In addition, the concentration factor of atrazine reached 250-fold with the optimized system (30 wt% glycerol + 50 wt% THF, corresponding to tie-line length 93.90). This concentration allowed the identification and quantification of atrazine in real samples of water collected in the basin hydrographic of the Japaratuba River, in the state of Sergipe, Brazil, which was previously diagnosed as being free of this compound, with values of 95 – 2400 ng.L-1 in surface water.