Anal. Chem.,1999, 71, 1176-82
Copyright © 1999 American Chemical Society
Effects of Chloride Ion Concentration on Mercury(I) Chloride Formation during ex Situ and in Situ Mercury Deposition with Selected Electrode Substrates and Electrolytes
Melissa A. Nolan and Samuel P. Kounaves*
Received for review July 27, 1998. Accepted January 6, 1999.
Abstract:
Ex situ and in situ mercury film formation was investigated in solutions containing
NO3-, SCN-, Cl-, and ClO4-,
and at glassy carbon macro- (3 mm) and micro- (10 mm)
electrodes, a platinum macro- (1.6 mm) electrode, and a microfabricated Ir-ultramicroelectrode
array (Ir-UMEA). The formation of mercury(I) chloride (calomel) during Hg deposition
was investigated by varying the Cl- concentration. The performance
of the Hg films was evaluated using Cd2+ and Pb2+ with
square wave anodic stripping voltammetry. For ex situ Hg film formation on Ir
and GC substrates, the highest efficiency was obtained when no Cl-
or 1 M Cl- was present. The Pt surface was affected by the Cl-
ions; thus for ex situ Hg film formation, the best results were obtained with
no Cl- present. Calomel formation during in situ Hg deposition occurred
for 0.001 > [Cl- ] < 0.5 M and was independent of the substrate.
Calomel interference was identified by the presence of an anomalous cathodic
peak between -0.6 and -0.3 V during the anodic scan. For in situ Hg film formation,
the Pb2+ stripping peak current increased with increasing ionic strength,
while the Cd2+ peak current increased dramatically in the presence
of SCN- or Cl-. Although conditioning of the Ir-UMEA and
Pt macroelectrode eliminated the cathodic peak, calomel still remained on the
surface after the Hg film was removed. When the cathodic peak was present, no
calomel remained after removal of the Hg film; thus for in situ film formation,
the calomel interference can be avoided. When [Cl-] > 0.01 M, the
best results can be obtained by adjusting [Cl-] to 1 M. For [Cl-]
< 0.01 M, addition of SCN- is recommended. Although analyses can
be preformed without any Cl- present, precautions should be taken
to avoid unintentional contamination.