Water samples were collected from a river (Gachsaran, Iran). Before the analysis, the samples were filtered through a cellulose membrane filter (Millipore) of pore size 0.45 lm. The organic content of the water samples were oxidized in the presence of 1% H2O2 and addition of concentrated HNO3. After acidification to 1% with concentrated nitric acid, they were stored in polyethylene bottles. For the preconcentration procedure, pH of the 800 mL of water samples was adjusted to 6. Then the preconcentration procedure given above was applied.