3.1. Cathodic stripping voltammetry of Mn complex
at pH 9.0
The effective interfacial accumulation of the Mn±
ammonium±acetate complex is examined after applying
the foregoing optimum experimental conditions at
different concentration levels, Fig. 3 displays Osteryoung
square-wave voltammograms for 410
ÿ9 M
Mn (0.22 mg l
ÿ1) after different preconcentration periods
from 0 to 300 s. Larger peak currents are
observed for longer accumulation periods.
Fig. 4 shows stripping voltammograms obtained for
manganese solutions of increasing concentrations,
after 30 s preconcentration time. Well-de®ned peaks
increase linearly with the manganese concentration
until its concentration reaches a value of about
110
ÿ6 M. This linearity is extended to about
210
ÿ5 M Mn, but with another slope indicating a
possible reorientation of the Mn complex at the electrode
surface during the adsorption process. The calibration
curves with and without preconcentration are
cited inside Fig. 4. Their characteristic features are
cited in Table 2. The reproducibility of the adsorption
process was tested at manganese concentration limit
of 110
ÿ6 M, well-de®ned reproducible peaks are
obtained after running the voltammogram 10 succes-