Thermo Scientific Dionex ICS-5000, Operator'S Manual

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2 • DC Description
Doc. 065342-06 12/11
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2.15.3 Palladium Hydrogen (PdH) Reference Electrode
The PdH reference electrode consists of palladium and platinum electrodes
immersed in an aqueous solution. With a potential applied between the two
electrodes, palladium is connected as a cathode and platinum as an anode. As
a consequence of the applied potential, hydrogen gas is generated at the
palladium electrode and oxygen gas at the platinum electrode. Whereas the
oxygen gas is swept out of the cell in the liquid stream, a portion of the
hydrogen gas is taken up by palladium metal. An equilibrium develops
between molecular hydrogen in the liquid phase and the adsorbed hydrogen in
palladium. The palladium hydrogen electrode becomes a reference electrode
with a half reaction of:
H
+
+ e- = ½ H
2
Where the hydrogen is supplied by the following process:
Pd + ½ H
2

Pd-H
ads

Pd-H
abs
The PdH reference electrode is thus similar to the standard hydrogen
electrode, which is based on the same half reaction between the hydronium
ions and molecular hydrogen. However, there are also some differences. For
example, palladium is not as good a catalyst for the electrode half reaction as
platinum. As a consequence, under identical conditions, the reference
potential of the palladium hydrogen electrode differs from that of the standard
hydrogen electrode by a constant potential. In addition, because hydronium
ions are involved in the reference half reaction, the potential of the PdH
electrode is pH dependent.
Waveforms for PdH Reference Electrodes in Chromeleon
When you create or edit an instrument method in Chromeleon 7 or a program
in Chromeleon 6.8, you can select a waveform created for use with the PdH
reference electrode. To use a waveform that was created for a pH-Ag/AgCl
electrode, select the waveform and then manually correct the potential values
in the Waveform Editor. The formula for correction is provided in the
Waveform Editor.
No pH Readout with the PdH Reference Mode
If the PdH electrode were connected to another reference electrode (for
example, a Ag/AgCl electrode), the PdH electrode could serve as a pH
indicator electrode. However, when the PdH electrode functions as a