eDAQ Picostat, Руководство пользователя

Страница: 102 / 122

98 eDAQ Potentiostats
The results show peaks (or steps) at different potentials than you expect.
• See previous section.
• Make sure the reference electrode is connected to the correct
(yellow) lead wire!
• Check the condition of the reference electrode. All reference
electrodes age. For example and Ag/AgCl electrode will age with
exposure to light. Eventually the white/light grey coating of AgCl on
the central silver wire will be replaced by a brown/black coating of
silver oxide. As this process takes place the apparent positions of
your voltammetric peaks will appear to shift to different potentials.
Most Ag/AgCl electrodes can be quickly regenerated by placing
the silver wire in 1 M hydrochloric acid solution for a minute or two
(any silver oxide is quickly reconverted to AgCl) — although you
may wish to remove the old coating completely and re–chloridize
the silver wire to ensure a good coating of fresh AgCl. Replace the
newly coated wire back into the electrode housing and refill with
freshly prepared KCl solution. Aged calomel (Hg/Hg
2
Cl
2
)
electrodes should usually be replaced. Reference electrodes using a
gelled electrolyte will deteriorate if the gel dries out.
The results are contaminated by ‘noise’.
• Most often the noise encountered in electrochemical experiments
is a manifestation of mains hum (50 or 60 Hz interference) from
power lines and mains–powered equipment. Note that, depending
on the sampling rate, aliasing can make such interference appear
as a low frequency oscillation superimposed on your data. Ensure
common grounding by attaching the
e-corder and computer to the
same power board which is then attached to a three pin (grounded)
power socket. If consistent with the bandwidth required by your
experiment, use the 10 Hz (or lower) filter of to record your results,
see
page 17 , page 37 , and page 55 . Get an electrical technician
to check that the grounding of the power socket itself is in good
condition. Try the Mains Filter setting (Chart and Scope software)
which is very effective at removing main induced artifacts
• Check electrode connections. Poor electrical contact to the
electrodes will act as a source of noise. Particularly check the
electrode cables: cables age, especially at the alligator clips where
they are subject to mechanical wear. Use a multimeter to ensure that
the clips are still in good electrical contact with the correct pins in