In the present study, we investigate the potentiometric behavior of Cu2+ carbon paste electrodes based on two mercapto compounds 2-Ethylmino-5-Mercapto-1,3,4-Thiadiazole (EAMT) and 2- Acetylamino-5-mercapto-1,3,4-thiadiazole (AAMT) self-assembled on gold nano-paricle (GNP) as ionophore. Then, the obtained results from the modified electrodes are compared. The selfassembled ionophores exhibit a high selectivity for Copper ion (Cu2+),in which the sulfur and nitrogen atoms in their structure play a significant role as the effective coordination donor site forthe Copper ion. Among these electrodes, the best performance was obtained with the sensor with a EAMT/graphite powder/paraffin oil weight ratio of 4.0/68/28 with 200 μL of GNP which exhibits the working concentration range of 1.6×10^−9 to 6.3×10^−2 M and a Nernstian slope of 28.9±0.4 mVdecade^−1 of copper (II) activity. The detection limit of electrode was2.9(±0.2)×10^−10M and potential response was pH , in other words, it was independent across the range of 2.8–6.3. The proposed electrode presented very good selectivity and sensitivity towards the Cu2+ ions over a wide variety of cations including alkali, alkaline earth, transition and heavy metal ions. Moreover, the proposed electrode was successfully applied as an indicator electrode in the potentiometric titration of Cu (II) ions with EDTA and also the potentiometric determination
of copper ions in spiked water samples.