Nanometer size materials have been used successfully for a wide range of technological applications including, bioelectronics, catalysis, optics, biomedical and chemical or biological sensors and biosensors[I,2], due to their catalytic properties and roughening of the conductive sensing interface. Cyclic voltammetry from CoCI2 natural aqueous solution produced a well defined cobalt oxide (CoOx) nanoparticles deposited on the surface of glassy carbon electrode [3,4]. The resulting electrode surfaces and its morphology were examined with both cyclic voltammetry and SEM. In continuous our studies for detection ultra trace amount of As3 [5) for the first time the electrochemical oxidation of arsenic at cobalt oxide nanoparticles modified GC electrode has been investigated. The modified electrode shows excellent catalytic activity toward arsenic oxidation at wide pH range, 5-1 1. The amperometric detection of arsenic is carried out at 0.75 V vs. Ag/AgCI reference electrode in phosphate buffer solution with pH 7. This modified electrode recedes many advantageous such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability of signal response during arsenic oxidation. In addition the interference effects various reducing compounds for signal response of As(11I) are negligible.
