Biomedical Engineering Reference
In-Depth Information
9.2 Intelligent Metal Sensing: The Psa Analyzer
In 1976, a new technique derived from polarographic methods, the potentiometric strip-
ping analysis (PSA), was proposed. This chemical method (60) is very sensitive for the
detection of metal ions in aqueous samples and consists of two steps: the ions are first elec-
trolytically concentrated by depositing them on a working electrode (preconcentration or
plating stage), and then a metal stripping phase follows, during which no control is per-
formed on the potential. The latter step is accomplished, usually with a chemical oxidant
in solution (Hg
or dissolved oxygen). After the preconcentration phase, the analytical
signal (the potential of the working electrode) is recorded as a function of time and then
utilized to obtain quantitative information about the metal ions in solution.
A recent paper (61) demonstrates the possibility to design and realize a simple and low-
cost instrument for monitoring environmentally significant metals by implementing the
PSA technique (Figure 9.1), connecting a cheap electronic device to a computer. Such
analyzer, suitable for heavy metal analyses (Figure 9.2), is based on the constant-current
potentiometric stripping analysis and on a very simple electrochemical cell. The software
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Me
n+
Me
V
bias
+
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Counter
Reference
Working
V
ref/wk
(a)
Multianalyte data acquisition
(Iox = 10 µA, acetate buffer 40 mM)
1
Lead
0.5
Copper
0
−
0.5
−
1
0
10
Time (s)
20
(b)
FIGURE 9.1
Schematic description of a PSA experiment. In (a), part 1, the electrochemical process taking place during the first
step is illustrated: the working electrode polarization causes the deposition of the metal ions on it; part 2 shows
the circuital schematics to drive this phase. Part (b) describes, in the same manner, the second step of the analyt-
ical technique.
