Page 112 - Analytical Electrochemistry 2d Ed - Jospeh Wang

EXAMPLES 97

From which an Fe(III) concentration of 1.47 ppb can be obtained for the sample.

Example 3-2 Calculate the limiting current that would be expected from the
2‡
reduction of 2 10 4 M Pb , using the DME characteristics m ˆ 2:0mg s 1 and
2
1
t ˆ 4 s. The diffusion coef®cient of Pb 2‡ is 1:01 10 5 cm s .
Solution The lead reduction is a two-reduction process:

Pb 2‡ ‡ 2e „ Pb
Hence, from the Ilkovic equation, (equation 3.3), we obtain

5 1=2 2=3 1=6
i ˆ 708 2 1:01 10 † 2:0† 4 0:2: ˆ 1:81 mA
d

Example 3-3 Draw clearly the DC polarographic response for a mixture contain-
2‡
2‡
ing 3 mM Cu ,2 mM Zn 2‡ and 1 mM Cd . The half-wave potentials for the Cu, Zn
and Cd ions are 0.12 V, 0.95 V and 0.62 V, respectively.
Solution