Amperometric detection of morphine at preheated glassy carbon electrode modified with multiwall carbon nanotubes

A highly sensitive and fast responding sensor for the determination of morphine is described. The multiwall carbon nanotubes immobilize on preheated glassy carbon electrode (5 min at 50 degrees C) by gently rubbing of electrode surface on a filter paper supporting the carbon nanotubes. The results indicated that carbon nanotubes(CNTs) modified glassy carbon electrode exhibited efficiently electrocatalytic oxidation for morphine with relatively high sensitivity, stability and long life. Under conditions of cyclic voltammetry, the potential for oxidation of morphine is lowered by approximately 100 mV and the current is enhanced significantly (10 times) in comparison to the bare glassy carbon electrode at wide pH range (2-9). The electrocatalytic behavior is further exploited as a sensitive detection scheme for morphine determination by hydrodynamic amperometry. Under the optimized conditions the calibration plots are linear in the concentration range 0.5-150 mu M with the calculated detection limit (S/N=3) of 0.2 mu M and sensitivity of 10 nA/mu M and a relative standard deviation (RSD) of 2.5% (n=10). The amperometric response is extremely stable, with no loss in sensitivity over a continual 30 min operation. Such attractive ability of multiwall carbon nanotubes (MWCNTs) modified GC electrode, suggests great promise for a morphine amperometric sensor. Finally the ability of the modified electrode was evaluated for simultaneous determination of morphine and codeine.