POTENTIOMETRIC STRIPPING ANALYSIS VS DIFFERENTIAL-PULSE ANODIC-STRIPPING VOLTAMMETRY FOR COPPER(II) ANALYSIS AT RELATIVELY POSITIVE DEPOSITION POTENTIAL

A comparative study of potentiometric stripping analysis (PSA) and dif ferential pulse anodic stripping voltammetry (DPASV) for copper analys is at relatively positive deposition potential, E(d) = -0.3 V vs. Ag/A gCl(s), 3 mol/l KCl, was carried out both in 0.01 mol/l KNO3, pH 6.5, and in a saline water (ionic strength ca. 0.5 mol/l, pH 7.5). A deposi tion time of 3 min was used. When a static mercury drop electrode was used as working electrode, PSA allowed determinations of copper in bot h media with the following limits of detection (LOD): 0.15 mu mol/l, f or 0.01 M KNO,, and 0.28 mu mol/l for saline water. DPASV allowed copp er determination in 0.01 M KNO3 with LOD = 0.18 mu mol/l, but not in t he saline water, because the baseline was not well-defined. When a thi n mercury film was used as the working electrode, the DPASV detection capability improved markedly in 0.01 M KNO3, LOD = 0.018 mu mol/l, but the determination of copper in the saline water was still unfeasible at E(d) = - 0.3 V. These results indicate that PSA can be applied to c opper analysis in saline waters at more positive deposition potentials than DPASV, but the LOD of PSA was too high to allow copper speciatio n in natural waters. In addition, it was verified that the presence in the solution of organic matter (humic acids 0.12 or 0.30 mg C/l), ads orbable at the working electrode, had no effect on the PSA signal, but markedly interfered in the DPASV response.