2 • DC Description
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pH–Ag/AgCl electrode also shifts by -0.059 V per pH unit, pH-dependent
potential shifts at the working electrode are canceled.
Correcting for pH Dependence
At an eluent pH of 7, the reference potential of the entire electrode is the
same as that of the Ag/AgCl half-cell. As the eluent pH is increased, the
pH half-cell potential decreases approximately 0.059 V per pH unit. For
example, at an eluent pH of 12, the reference potential of the pH half-cell
would be -0.295 V relative to the Ag/AgCl half-cell. Therefore, at pH 12,
the potentials applied to the working electrode must be raised
approximately 0.3 V when switching from the “Ag” reference to the “pH”
reference.
In acidic eluents, the reference potential of the pH half-cell is positive
with respect to the Ag/AgCl half-cell, and all applied potentials must be
decreased by 0.059 V per pH unit when switching from the “Ag”
reference to the “pH” reference.
Monitoring the Amperometry Cell pH Readout
Monitoring the pH readout of a solution with a known composition lets
you detect any reference potential shift that may occur over time. This
allows you to determine when the reference electrode needs regenerating
or replacing, thus improving the reproducibility of your analyses. See
Section 4.1.2
for how to monitor the pH readout.
NOTE Monitor the pH when the reference electrode is used in
the Ag mode as well as in the pH mode.
Do not allow the reference electrode to dry out. Make sure that eluent
is being pumped continuously through the cell. If the cell will not be
used for a short time (less than 2 days), disconnect the tubing from
the inlet and outlet fittings and install fitting plugs. For longer
shutdowns, remove the electrode from the cell and store it in its
storage cap filled with saturated KCl solution. See Section 6.4
for
detailed storage instructions.
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