Determination of copper in fuel ethanol for car engines by anodic stripping voltammetry

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The presence of copper in fuel ethanol blends has gained considerable attention, since Cu2+ catalyzes oxidative reactions in gasoline leading to a deterioration of olefins and the formation of gum. Anodic stripping voltammetry (ASV), one of the most sensitive and accurate techniques for trace-metal analysis, has been demonstrated for the determination of Cu(II) in ethanol/gasoline blends without any sample pretreatment. Copper ions are first electrodeposited onto the surface of a hanging mercury drop electrode (HMDE) before the amalgamated copper is quantitatively stripped (anodically dissolved), a current-voltage curve being recorded.Experimental conditions such as deposition time and potential as well as the suitable electrolyte and reference electrode were determined in preliminary experiments. For synthetic samples spiked with Cu2+ (5…100 µg/L), recovery rates between 96 and 112% were obtained. The copper-spiked E85 sample provided a recovery of 100%. The relative standard deviations for Cu2+ concentrations of 5 µg/L and above were 8.0 and 5.5% respectively. Using a preconcentration time of 60 s at -0.7 V versus Ag/AgCl, a linear range of 0…500 µg/L with a detection limit of 2 µg/L was obtained.