124
Problem
Suggested Cause or Action
Electrical Noise
in Voltammograms
(brush wear)
Always use a banana jumper cable to connect opposing
brushes together. Two brushes in opposing contact
provide a better electrical connection.
Inspect all brush contacts. Brushes should have a
concave groove worn in them which exactly mates with
the rotating shaft. The depth of this concave groove
naturally increases over the lifetime of the brush. A new
brush should be worn continuously for approximately
eight hours to intentionally wear a groove into the brush
to increase the surface area of the brush that is in contact
with the shaft.
Electrical Noise
in Voltammograms
(cell connections)
Confirm that the reference electrode has low impedance
and is in good contact with the main test solution. High
impedance at the reference electrode is often caused
by a plugged frit, which impedes current between the
inner chamber of the reference electrode and the main
test solution. High impedance may also be encountered
when working with low dielectric media (such as non-
aqueous solvents).
Use working, reference, and counter electrode cables
which are shielded (coaxial) cables.
Confirm that any alligator clips being used for connection
to the electrodes are not corroded and are securely
fastened to the electrodes.
Note that many potentiostats utilize a driven shield to
protect the reference electrode signal. This driven shield
is connected to the outer shield line in the coaxial
reference electrode cable. Only the inner signal line of
the coaxial cable should be connected to the reference
electrode. The outer shield line should not be connected
to anything at the cell end of the cable. Do not ground
such a driven shield line as it may cause the potentiostat
to oscillate or malfunction.
Summary of Contents for MSR 636A
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