he choice of the deposition potential can provide some
selectivity in the measurement (see Figure 2). In
considering a dc polarogram of lead and cadmium as a
comparison, this figure shows the first plateau as the
diffusion-limited current due to the reduction of lead.
The second plateau is due to the diffusion-limited current
of both lead and cadmium. Deposition at potential A
yields stripping peak A for lead. There is no contribution
to the stripping voltammogram from the cadmium in
solution since deposition at this potential reduces lead
only. Deposition at potential B yields stripping peak B.
The peak is somewhat higher but there still is no
contribution from the cadmium in solution. Finally,
deposition at potential C yields two stripping peaks on
curve C. The peak at about -0.6 V corresponds to
cadmium since deposition at potential C is negative
enough to reduce cadmium and lead simultaneously. As
is obvious from Figure 2, the deposition potential is most
appropriately chosen by running a polarogram of a
concentrated solution (10-20 ppm) of the analyte.