Anal. Chem., 71 (
Web Release Date: July 2,
Copyright © 1999 American Chemical Society
Microfabricated Array of Iridium Microdisks as a Substrate
for Direct Determination of Cu2+ or Hg2+ Using Square-Wave
Anodic Stripping Voltammetry
Melissa A. Nolan and Samuel P. Kounaves* Department of Chemistry, Tufts University, Medford, MA
02155
Received for review February 5, 1999. Accepted May 25, 1999.
Abstract:
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.