Gamry Instruments Interface 1000, Руководство оператора

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Chapter 8: Measurement of Small Signals--Hints for System and Cell Design
8 - 6
In these cases, the capacitance between the Interface 1000 cell leads can result in an error. The Interface
1000 alligator clips can have 10 pF or more of mutual capacitance if they are run alongside each other.
If you wish to avoid excessive capacitance:

Place the leads as far apart as possible. Pay special attention to physical separation between
the working electrode and working sense leads and the counter/ counter sense/reference
electrode leads.

Have the leads approach the cell from different directions.

Remove the alligator clips from the leads. In extreme cases you can replace the banana plugs
and pin jack with smaller connectors. If you do so, be careful not to compromise the isolation
between the center conductor and the shield.
The cell leads must not be moved during an experiment measuring small currents. Both microphonic and
triboelectric effects can create spurious results when the cell cables are moved.
Cell Construction
If you need to measure small currents or high impedances, make sure that your cell construction does not
limit your response.
A cell where the resistance between the electrodes is only 10 10 Ω cannot be used to measure an
impedance of 10
13
Ω. In general, glass and Teflon
®
are the preferred materials for constructing cells. Even
glass may be a problem when it is wet.
You also must consider C
shunt
. Make the “inactive” portion of your electrodes as small as possible. Avoid
placing electrodes close together or parallel with each other if you are measuring high impedances.
Reference Electrode
Keep the impedance of your reference electrode as low as possible. High-impedance reference electrodes
can cause instability of the potentiostat and excessive pick-up of voltage noise.
Avoid:

Narrow-bore or Luggin capillaries tipped with glass frit.

Poorly conductive solutions, especially in Luggin capillaries.

Asbestos-thread and double-junction reference electrodes.
Reference electrodes often develop high impedances as they get used. Anything that can clog the isolation
frit can raise the electrode impedance. Avoid using saturated KCl-based reference electrodes in solutions of
perchlorate ions.
Instrument Settings
When setting up a very sensitive experiment,

In EIS, use the largest practical excitation. Don’t use a 10 mV excitation on a coated specimen
that can handle 100 mV without damage.

Avoid potentials where large DC currents flow. You cannot measure 1pA of AC current on top
of 1 mA of DC current.
EIS Speed
In EIS, do not expect the Interface 1000 to measure 10
10
Ω impedances at 1 kHz. Many of the factors
listed above limit the performance.
As a rule of thumb, the product of impedance, Z , times frequency, f, should be less than 10
9
Ω ∙ Hz for good
EIS measurements with an Interface 1000, i.e.,
Z · f < 10 9 Ω ∙ Hz