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 Cu 2+ and Hg 2+ 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 Cu 2+ in the 20−100 ppb range and for Hg 2+ in the 1−10 ppb range when the bare iridium substrate was used. Detection limits were calculated to be 1 ppb (0.1 M KNO 3 and 0.1 M HClO 4, deposition time 180 s) and 5 ppb (0.1 M H 2 SO 4, deposition time 120 s) for Cu 2+ (S/N = 3) and 85 ppt for Hg 2+ (deposition time 600 s). The experimental detection limits were determined to be 5 ppb for Cu 2+ (deposition time 180 s) and 100 ppt for Hg 2+ (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.