10-22
Sampled Current Polarography (
SCP
) or Tast polarography is a modification of the
classical D.C. polarography experiment, and was designed to reduce the effect the
changing surface area of the mercury drop. The potential wave form is shown in
Figure 10-10. The potential is varied in a series of steps (it is held at each step for the
Drop Time
), and the current is sampled at the end of each drop. The
Drop Time
and
the size of the potential step can be varied (through variation of the
Scan Rate
). This
potential waveform is often referred as a staircase waveform.
-E
SAMPLING WIDTH
STEP
DROP TIME
QUIET TIME
t
Figure 10-10.
Potential wave form for
SCP
.
The current response is shown in Figure 10-11. The limiting current (i
d
) is given by
the Ilkovic equation:
Figure 10-11.
Typical current response for
SCP
.
i
d
= 708nD
1/2
Cm
2/3
τ
1/6
where: n = number of electrons transferred/molecule
D = diffusion coefficient (cm
2
/s)
m = mercury flow rate (mg/s)
τ
= sampling interval (s)
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