Metrohm 781 pH/Ion Meter - Manual (Page 136)

8.6 pH electrode test
126
780/781 pH/Ion Meter, Manual
8.6 pH electrode test
With the pH/Ion Meter you can carry out an automatic pH electrode test
which allows the quality of the electrode used to be evaluated. As the
result you will obtain various information about the characteristic meas-
uring properties of your pH electrode (slope, response time, drift,
streaming potential). The concluding evaluation of the electrode is car-
ried out by checking the results obtained against preset tolerances.
These tolerances are stored in the pH/Ion Meter for the three most fre-
quently used types of Metrohm pH electrodes: standard electrodes, gel
electrodes and non-aqueous electrodes. You can also define your own
limits. The specific classification of the electrode system is defined by
the reference system used. You find overview for these electrode types
and the corresponding tolerances on p. 130.
In the electrode test faulty electrodes frequently show certain combina-
tions of measured results which lie outside the preset limits. This per-
mits more detailed information to be given about possible causes and
recommended measures.
8.6.1 Preparations
Buffers
You need faultless pH 4, pH 7 and pH 9 buffers for carrying out the
electrode test. We recommend the use of suitable Metrohm buffers. In
principle the electrode test can also be carried out with any of the
stored sets of buffers which contain buffers with these values. The set
of buffers used must be set in the calibration parameters (see also Sec-
tion 6.2.2):
PARAMETER pH
:
├
calibration parameters
: :
├
buffer type
:
If an electrode test is started with a set of buffers which does not con-
tain the necessary buffers then the following error message will appear:
buffers unsuitable
Particularly with buffer pH 9 you should make certain that it is in a
faultless condition. By absorption of CO
2
from the atmosphere this
buffer can easily vary from its specified pH values and therefore pro-
duce incorrect test results.
Stirrer
You require a stirrer for the test. We recommend the use of a Metrohm
stirrer as this allows the electrode test to be carried out automatically.
Information about the connection and configuration of such a stirrer is
given in Section 5.6.
EL.TEST
1