Ionode IJ pH V5.1 - Manual (Page 34)

Ionode IJ Instruction Manual 34
5.2. Measurement
Unlike a pH electrode, an ORP electrode does
not require asymmetry potential and slope
corrections However, it can develop an offset
depending on the cleanliness of the sensing tip
and reference junction. It should be checked
periodically in standards.
1) Set the pH/mV meter to mV mode.
2) Connect the electrode to the pH/mV meter.
Rinse thoroughly with deionised water.
3) Place the electrode in an ORP standard.
Measure the temperature and determine
the potential (see
Table 7 - Table 9 ). Note
that ORP standards have significant
temperature coefficients. Allow the reading
to stabilize. It should be within +/-20 mV of
the correct value (see 5.4 Calibration
Standards). If not, clean the electrode as
described in 4.4.1
Cleaning and replenish
the sleeve electrolyte. Repeat the check.
4) Rinse with deionised water.
5) Place the electrode in the sample and stir.
Most irreversible redox couples require
vigorous stirring to attain a plateau
response. Lack of adequate stirring usually
results in a lower potential
6) Allow the reading to stabilize and record.
5.2.1. Helpful Hints
1) ORP samples are generally unstable and
should not be stored or preserved. Measure
samples on site whenever possible.
2) Clean the sensing tip regularly (see 4.4.1
Cleaning ). An unclean sensing tip is the
most common cause of error in ORP
measurement.
3) Allow adequate time for stabilization,
especially between samples of considerably