Metrohm 817 Bioscan - Manual (Page 57)

4.3 Pulsed amperometric detection
817 Bioscan
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4.3 Pulsed amperometric detection
During an amperometric determination the reaction products formed on
the working electrode can alter its surface properties by adsorption. In
pulsed amperometric detection (PAD) it is possible to apply further po-
tentials cyclically in addition to the detection potential in order to ensure
a constant electrode surface. In this way the electrode surface is re-
newed after each current measurement and remains in this activated
condition.
The exact potential steps are shown in Fig. 11 as a function of time.
Fig. 11: Potentials applied during pulsed amperometric detection (PAD)
The working potential E1 is applied during the time t1 with the signal
being measured in ts. The high positive potential E2 causes the oxida-
tive removement of reaction products from the electrode surface, which
is reduced to a pure Au-surface during t3.
4.3.1 Optimization of the PAD parameters
When adapting the method parameters the preset parameters should
initially be used. Descriptions of various applications are available from
Metrohm AG in the form of Application Works and Application Notes.
These can be obtained from your local Metrohm agency or on the Inter-
net under
www.metrohm.com .
The potential profile shown in Fig. 11 must always be matched to the
analyte under investigation. 7 parameters must be taken into account:
potentials E1, E2 and E3, time intervals t1, t2 and t3 and the measuring
time ts. Some basic conditions are preset; this makes configuration
easier. These are described below.
2.0 1.0