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 separa te electrochemical determinations of Cu2+ and Hg2+ directly on a microlitho graphically fabricated array of iridium ultramicroelectrodes (Ir-UMEA). Squ are-wave anodic stripping voltammetry was used to optimize experimental par ameters such as supporting electrolyte, square-wave frequency, and depositi on time and potential. Reproducible stripping peaks were obtained for solut ions 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. Detect ion limits were calculated to be 1 ppb (0.1 M KNO3 and 0.1 M HClO4, deposit ion 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 detect ion 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 perfor med, and it was determined that Pb, Zn, and Cd had little or no influence o n the copper signal. Tap water and spring water samples were analyzed for c opper, and good agreement was obtained with conventional methods. An unexpl ained effect of chloride ions on the iridium surface was noted. Further inv estigation;by atomic force microscopy determined that changes on the surfac e 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 chemicall y harsh environments.