Microfabricated array of iridium microdisks as a substrate for direct determination of Cu2+ or Hg2+ using square-wave anodic stripping voltammetry

In this paper, we report for the first time the characterization and separate electrochemical determinations of Cu2+ and Hg2+ directly on a microlithographically fabricated array of iridium ultramicroelectrodes (Ir-UMEA). Square-wave anodic stripping voltammetry was used to optimize experimental parameters such as supporting electrolyte, square-wave frequency, and deposition time and potential. Reproducible stripping peaks were obtained for solutions containing low parts per billion (ppb) concentrations of either metal. Excellent linearity was obtained for Cu2+ in the 20-100 ppb range and for Hg2+ in the 1-10 ppb range when the bare iridium substrate was used. Detection limits were calculated to be 1 ppb (0.1 M KNO3 and 0.1 M HClO4, deposition time 180 s) and 5 ppb (0.1 M H2SO4, deposition time 120 s) for Cu2+ (S/N = 3) and 85 ppt for Hg2+ (deposition time 600 s). The experimental detection limits were determined to be 5 ppb for Cu2+ (deposition time 180 s) and 100 ppt for Hg2+ (deposition time 600 s). Interference studies were performed, and it was determined that Pb, Zn, and Cd had little or no influence on the copper signal. Tap water and spring water samples were analyzed for copper, and good agreement was obtained with conventional methods. An unexplained effect of chloride ions on the iridium surface was noted. Further investigation;by atomic force microscopy determined that changes on the surface occurred but could be eliminated when chloride leakage from the reference electrode was minimized. The solid state construction of the Ir-UMEA makes it a prime candidate for use in determining Cu(II) and Hg(II) in chemically harsh environments.