Anodic stripping voltammetric determination of copper (II) ions using a graphene quantum dot Modified pencil graphite Electrode

Copper is essential to all living organisms as a trace nutritional mineral because it involves in the synthesis of hemoglobin, a variety of enzymes, and the metabolism of the body [1-3]. However, copper deficiency or elevated levels of copper can bring about opposite health effects. Due to physiological importance of copper and widely usage of it in industrial and agricultural sectors, determination of copper in various matrices is very important and numerous analytical techniques have been used for the accurate and sensitive determination of trace quantities of copper [4-10]. Among these, electrochemical techniques have attracted extra attention because of many advantages such as simplicity, cost effectiveness, small instrumentation and etc. Graphene quantum dots (GQDs), a new kind of carbon nanomaterials, with great surface area and quick electron transfer ability are one of the best electrode modifiers which can increase the rate of electrochemical reactions and attracted more attention as electrode modifier [11]. Recently, Wang et. al developed graphene quantum dots as a fluorescent sensing platform for highly efficient detection of copper (II) ions [12]. In this work, we described a simple and sensitive electrochemical approach for the determination of low concentration of Cu2+ ions using GQD modified pencil graphite electrode by square wave adsorptive stripping voltammetric method. The sensing mechanism could be attributed to the formation of complex between Cu2+ ions and oxygen containing groups in GQDs which result in increased SWV signal compared to bare electrode. Optimization of various experimental parameters such as pre-concentration time, preconcentration potential, pH, and buffer type which influenced the performance of the sensor, were investigated. Under optimized condition, GQD modified electrode was used for the analysis of Cu2+ in the concentration range from 0.05 to 4 nM, and a lower detection limit of 0.012 nM with 319 good stability, repeatability, and selectivity. Finally, the practical applicability of GQD-PGE was confirmed via measuring trace amount of Cu (II) in water samples. The GQD-PGE surface could be regenerated by exerting more positive potential than the stripping potential of the Cu (II) ion and then used for another deposition. This is the first usage of untreated graphene type nano particles, GQD, for the simple, cheap, sensitive and selective determination of copper ions with excellent performance and low detection limit.