Easy modification of pencil graphite electrode for discrimination and determination of morphine in biological and street samples

The electrochemical sensor was developed for discrimination and determination of morphine (MO) using an electrochemically pretreated pencil graphite electrode (PPGE). A potentiostatic strategy was employed for the electrochemical pretreatment of the electrode. The PPGE has displayed very good electrochemical catalytic activities as compared with the non-pretreated PGE (NPGE). At the PPGE, two well-defined anodic peaks of morphine at about 0.35 V and +0.80 V were observed. There is only a weak oxidation peak at +0.50 V at NPGE at the same morphine concentration, while the peak cannot be found at +0.80 V. The pretreatment of the polished PGE by electrostatic procedure at 1.80 V for 5 min in 0.50 M phosphate buffer solution of pH 7.0 was proposed as the optimum pretreatment procedure. Differential pulse voltammetry (DPV) and hydrodynamic amperometry were used for determination of MO. A calibration graph plotted by the variation of anodic peak currents as a function of MO concentration was linear in the range of 1-100 mu M. The detection limit calculated from calibration graph was 0.26 mu M. The PPGE was used for determination of MO in real samples, including human urine and street drug samples such as opium, heroin and heroin-crack, and the results were quite promising.