A new approach for nitrite amperometric determination was studied using carbon paste electrodes based on poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels modified with two different Toluidine Blue (TBO) concentrations (480 mmol/ml and 960 mmol/ml). All, the electrochemical and electroanalytical characteristics of the obtained electrodes were investigated comparatively. The prepared modified electrodes showed good electrocatalytic effect towards nitrite oxidation. Most common ions do not interfere. The obtained sensor has a linear response in the concentration range of 1 mu M to 1 mM, a sensitivity of 0.06 A M-1 and a detection limit of 4.4 mu M (in phosphate buffer pH 7). The as obtained nitrite sensors were successfully used for nitrite determination in freshwater samples (groundwater and surface water), using standard addition method. (C) 2017 Elsevier B.V. All rights reserved.