eDAQ Picostat, User Manual

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Chapter 5 — Techniques 75
current signal may be dominated by the low-pass filter time response
characteristics. The base potential is adjusted with the Output Voltage…
command (Setup menu) shown in
Figure 5–13 .
A potential that will cause the reaction to proceed (and the period for
which it will be applied) is set using the Stimulator command. In the
example shown in
Figure 5–13 , after a period of 10 s at the base
potential of +0.5 V, two 30 s pulses of –0.70 V are to be applied each
followed by a 30 s return to the base potential.
The experiment is usually first done on a blank solution containing only
electrolyte, followed by a sample solution containing the substrate. The
data is collected on separate pages in Scope and the ‘blank’ data
subtracted with the Set Background command. You can then copy and
paste the scan to a spreadsheet so that the differences can be plotted
against 1/√t in a Cottrell graph.
For further details refer to the Scope Software Manual .
Chronocoulometry
Chart and Scope software have the ability to integrate an incoming
signal both online (that is, in real time as you are collecting data), or
offline (that is after the experiment is completed). Since the total charge
transferred (the total number of coulombs, or electrons, transferred) is
equal to the integrated current, the settings used for
chronoamperometry,
page 65 , can also be used for chronocoulometry.
With Chart software it also necessary to set up an unused channel
(usually Channel 3) to be the integral of the current signal channel
(usually Channel 1).
With an online function you need to actually be recording data to
obtain the integral. To configure Channel 3 you need to choose the
Computed Input command from the Channel Function pop-up menu,
which opens the Computed Input dialog box (
Figure 5–14 on a
Windows computer, and Figure 5–15 on a Macintosh). For more
information refer to the Computed Input section in the Chart Software
Manual .
Post-acquisition integration of a signal is also possible with the Chart
Integral channel calculation, which is accessed via the Integral