Metrohm 871 Advanced Bioscan - Manual (Page 25)

3.3 Pulsed amperometric detection
871 Advanced Bioscan / Instructions for Use 8.871.1003
17
a displacement of the characteristic current/poten-
oltammograms). Possible results are
ity and lower sig-
ensure that a stable
baseline and reproducible measuring conditions are
ned care should be taken that the pH of the
Pulsation Electrochemical reactions at the electrode surfaces
depend on the transport of the reacting substances
to the electrode. This is why a constant eluent flow
is crucial, both for a stable baseline and also for re-
supply must be ensured. You should use the pulsa-
tion absorber provided (see Section 2.4.3).
3.3 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 Figure 5 as a function of time.
tial curves (v
the reduction of the signal intens
nal/noise ratios. In order to
obtai
eluent is correct.
•
producible signals. This is why pulsation-free eluent
Figure 5: 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 reconditioned surface during t3.
2.0 1.0