Metrohm 916 Ti-Touch - Manual (Page 354)

28.7 Electrode test for pH electrodes (ELT)
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916 Ti-Touch
28.7 Electrode test for pH electrodes (ELT)
An automatic electrode test can be carried out for pH electrodes which
will permit a qualification of the electrode used. Differentiated specifica-
tions regarding characteristic measurement properties of your pH elec-
trode (slope, response time, etc.) will be obtained as the result. The con-
cluding evaluation of the electrode is carried out by testing these results
against the specified limit values. Once the electrode test has been suc-
cessfully completed, the calibration data is stored with the sensor data of
the sensor used.
These limit values are saved in the software for the following types of pH
electrodes:
￭ Standard electrodes
￭ Gel electrodes
￭ Electrodes with a non-aqueous reference electrolyte
You can however also define limits of your own choosing (see Chapter
15.7, page 167). The precise classification of the measuring chain is deter-
mined by the reference system used. You will find an overview of these
electrode types and the corresponding limit values in table 10, page 342.
Faulty electrodes often exhibit certain combinations of measurement
results of the electrode test which fall outside the intended limits. This
makes it possible to have more precise data concerning possible causes of
errors and recommended remedial measures.
Buffers
You will require flawless buffers in the pH values 4, 7 and 9 for carrying
out the electrode test. We recommend for this purpose the appropriate
Metrohm buffers. The electrode test can however in principle also be car-
ried out with any of the buffer sets contained in the memory.
The buffers must be measured in the following sequence:
1. pH 9
2. pH 4
3. pH 7
NOTE
Ensure in particular the flawlessness of the pH 9 buffer. It can readily
deviate from its specified pH value as the result of absorption of CO
2
from the ambient atmosphere, thus leading to incorrect test results.