ICS-3000 Ion Chromatography System
58 Doc. 065031-04 1/08
Cell Design
The ED amperometry cell is a thin-layer design. Eluent flows in a thin
channel parallel to the surface of a flat disk electrode. The resulting
smooth flow minimizes noise. The low volume (0.25
μL) of the channel
also allows operation with high efficiency, narrow bore columns. The cell
design minimizes the electrical resistance between the working electrode
and the counter electrode by positioning the counter electrode (the cell
body) directly across the thin-layer channel from the working electrode.
This results in a wide linear dynamic range. The inlet tubing is in
electrical contact with the counter electrode and through it to ground. The
working electrode current is processed using low noise analog amplifiers
and filters.
Amperometry Cell Solvent Compatibility
The amperometry cell can be used with common reversed-phase solvents
such as methanol and acetonitrile. If a disposable working electrode is
used, the percentage of methanol should not exceed 30% and the
percentage of acetonitrile should not exceed 10%. Refer to the disposable
electrode manual (Document No. 065040) for additional eluent
compatibility information. Because conventional working electrode
blocks are made of Kel-F® and use a gasket made of Ultem®, there is no
restriction on the concentration of organic solvents that can be used with
them.
2.16.2 Combination pH–Ag/AgCl Reference Electrode
The reference electrode is a standard combination pH electrode
containing a glass membrane pH half-cell and a Ag/AgCl half-cell. The
combination pH electrode monitors eluent pH.
The Ag/AgCl half-cell is typically used as the cell reference electrode. To
minimize changes in the baseline, the combination pH–Ag/AgCl
electrode can be used as the reference electrode during a pH gradient.
pH Dependence
The potentials at which many redox reactions take place on metallic
electrodes are pH-dependent, with the potential shifting -0.059 V per pH
unit. This is especially true for metal oxide formation, oxidation, and
oxidative desorption. Since the reference potential of the combination
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