eDAQ Picostat, Руководство пользователя

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Chapter 5 — Techniques 87
polarising voltage (applied potential) of between –0.7 to –0.8 V is
required at the working electrode to effect the reaction:
The exact potential can be varied to suit the sample being measured
and to minimise side reactions. A smaller potential reduces sensitivity
but is usually more selective for oxygen.
Most oxygen sensors exhibit a slow response time and will take at least
several seconds to stabilise. Thus you would normally employ a
1 – 10 Hz filter setting on the Potentiostat, QuadStat, or Picostat in
order to minimise any electrical noise. The Mains Filter setting can also
be employed to further reduce mains hum. Sampling rates of about
1 /s are usually optimal.
The QuadStat also has the ability to zero (or offset) a background
current signal which can be of use when trying to amplify small peaks
on a large background signal, see
Zero Offset, page 57 .
If you intend to monitor oxygen concentrations over a wide range then
you can calibrate the electrode at several concentrations and use the
Chart software Multiple Point Calibration extension to compensate for a
non-–linear electrode response. You can download the extension from
www.edaq.com.
Nitric Oxide (NO) Sensors
Most polarographic nitric oxide sensors can be used with the Picostat,
or QuadStat, which are suitable for detecting the small currents
expected from the low concentrations of nitric oxide found in natural
biological systems.
Most commercial nitric oxide sensors comprise a carbon fibre anodic
working electrode (to which the working electrode lead is attached)
and a cathodic counter electrode (to which the reference and auxiliary
electrode leads are attached). Usually an oxidising polarising voltage
O
2
4H
+
4e
–
2H
2
O
→
+ +