Page 88 - Analytical Electrochemistry 2d Ed - Jospeh Wang
P. 88
3-3 PULSE VOLTAMMETRY 73
FIGURE 3-9 Square-wave voltammograms for reversible electron transfer. Curve A:
forward current. Curve B: reverse current. Curve C: net current. (Reproduced with permission
from reference 9.)
The major advantage of square-wave voltammetry is its speed. The effective scan
rate is given by f DE . The term f is square-wave frequency (in Hz) and DE is the
s
s
step height. Frequencies of 1 to 100 cycles per second permit the use of extremely
fast potential scan rates. For example, if DE 10 mV and f 50 Hz, then the
s
1
effective scan rate is 0.5 V s . As a result, the analysis time is drastically reduced; a
complete voltammogram can be recorded within a few seconds, as compared with
about 2±3 minutes in differential-pulse voltammetry. Because of the fast scan rates,
the entire voltammogram is recorded on a single mercury drop. Hence, such an
operation consumes few drops (compared to other pulse techniques). The inherent
speed of square-wave voltammetry can greatly increase sample throughputs in batch
(11) and ¯ow (12) analytical operations. In addition, square-wave voltammetric
detection for liquid chromatography and capillary electrophoresis can be used to
