eDAQ Picostat, User Manual

Page: 92 / 122

88 eDAQ Potentiostats
(applied potential) of up to +1.0 V is required at the working electrode,
to effect the reaction:
The exact potential can be varied to suit the type of electrode (many
electrodes have special catalytic surface coatings), the sample being
measured, and to minimise side reactions. At potentials smaller than
+0.7 V, the current signal is usually dependent on the polarising
voltage, but b0.7 and +1.0 V the current signal tends to
plateau as the reaction is limited by the rate at which nitric oxide can
diffuse to the anode surface. At potentials greater than +1.0 V the
hydrolysis of water gradually becomes the dominant source of the
current signal.
Most nitric oxide 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 in order to minimize 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.
It is recommended in most cases to calibrate the electrode at several
nitric oxide concentrations covering your range of interest. Use the
Chart software Multiple Point Calibration extension which can be
downloaded from the eDAQ web site at www.edaq.com.
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 .
NO 2H
2
O NO
–
3
4H
+
3e
–
+ +
→
+