Silica‐modified carbon paste electrode for copper determination in ammoniacal medium

Abstract

AbstractThe silica modified carbon paste electrode (SMCPE) was applied to the voltammetric detection of copper(II) at trace level after its accumulation under open‐circuit conditions. As demonstrated by cyclic voltammetric experiments, silica particles displayed an attractive ability to efficiently preconcentrate trace copper(II) from ammonia solution, according to a combined acid‐base and complexation reaction: 2 (SiOH) + Cu(NH3) ⇌ (SiO)2Cu(NH3)2 + 2 NH. The analytical procedure involved four successive steps: the preconcentration during a given period of time at open circuit in the ammoniated analyte solution, the medium exchange of the electrode (washed with water) to a pure electrolyte solution (0.1 M HNO3), a 30 s electrolysis for reducing the accumulated CuII species, and the square wave voltammetric determination. Experimental parameters affecting either the uptake of copper(II) or its voltammetric detection at SMCPE were explored, including the solution pH and ionic strength, the ammonia concentration in the preconcentration medium, the preconcentration time, the deposition potential and duration, the anodic stripping scan mode or the silica loading into the paste. A detection limit of 2 × 10−9 M has been achieved after 10 min preconcentration (from a 0.5 M NH3 medium), as determined for a signal‐to‐noise ratio of 3, and a linear calibration plot was obtained in the 5 × 10−9 M to 5 × 10−6 M concentration range. The relative standard deviation (n = 8) for the determination of a 5 × 10−7 M Cu11 sample was 8%.