Differential pulse anodic stripping voltammetric determination of traces of copper with a tobramycin-Nafion modified electrode.
A Nafion-modified glassy carbon electrode incorporated with tobramycin for the voltammetric stripping determination of Cu2+ has been explored. The electrode was fabricated by tobramycin containing Nafion on the glassy carbon electrode surface. The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu2+ compared with a bare glassy carbon electrode and the Nafion modified electrode. Cu2+ was accumulated in HAc-NaAc buffer (pH 4.6) at a potential of -0.6 V (vs. SCE) for 300 s and then determined by differential pulse anodic stripping voltammetry. The effects of various parameters, such as the mass of Nafion, the concentration of tobramycin, the pH of the medium, the accumulation potential, the accumulation time and the scan rate, were investigated. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 1.0 x 10(-9) to 5.0 x 10(-7) mol l(-1) with a correlation coefficient of 0.9971. The relative standard deviations for eight successive determinations were 4.3 and 2.9% for 1.0 x 10(-8) and 2.0 x 10(-7) mol l(-1) Cu2+, respectively. The detection limit (three times signal to noise) was 5.0 x 10(-10) mol l(-1). A study of interfering substances was also performed, and the method was applied to the direct determination of copper in water samples, and also in analytical reagent-grade salts with satisfactory results.
Accumulation voltammetry of copper(II) using a carbon paste electrode modified with di-8-quinolyl disulphide
The accumulation voltammetry of copper(II) was investigated with a carbon paste electrode modified with di-8-quinolyl disulphide (DQDS). The DQDS was reduced to quinoline-8-thiol by applying a suitable potential. Copper(II) was accumulated on the electrode as the copper(II)-quinoline-8-thiol complex at a constant potential in 0.1 mol dm–3 acetate buffer. The reduction peak of the copper(II) complex was then observed at –0.30 V by scanning the potential in a negative direction using the differential-pulse mode. The calibration graph for copper(II) was linear over the range 3 × 10–9–2 × 10–6 mol dm–3 with accumulation for 5 min at –0.05 V. As copper(II) was selectively accumulated on the electrode, the influence of concomitant ions was negligible. The method was applied to the determination of copper(II) in Geological Survey of Japan rock reference materials.
Chitin and chitosan as chromatographic supports and adsorbents for collection of metal ions from organic and aqueous solutions and sea-water.
The rates of adsorption of several metal ions on chitin and chitosan in water and sea-water have been measured; chitin and chitosan are proposed as Chromatographic chelating supports. These natural polymers are also suitable for recovery of trace metals from sea-water.