Metrohm 781 pH/Ion Meter - Manual (Page 123)

8 Troubleshooting – Messages – Maintenance
780/781 pH/Ion Meter, Manual
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8 Troubleshooting – Messages –
Maintenance
8.1 Troubleshooting
If problems occur during pH or ISE measurement then these can have
various causes:
1. Application
Difficult sample matrices or interferences can prevent reliable meas-
urements (e.g. insufficient ionic strength, presence of interfering ions
in ISE measurements, etc.). Our Application Bulletins and Applica-
tion Notes support you in correct selection of the analytical condi-
tions and the configuration of the instrumental method.
2. Buffer / Standard solution
The precision of pH and ion measurements depends primarily on
the correction calibration of the electrode. You should use clean and
fresh buffer solutions and standard solutions. For example, a fre-
quent cause of incorrect calibration is the use of an old pH 9 or pH
10 buffer, whose pH can vary considerably from the certified pH of a
new buffer as a result of the absorption of atmospheric CO
2
.
3. Measuring / Reference electrode
The electrodes are the most important element of the whole measur-
ing system. The correct handling of the measuring and reference
electrodes is described in the leaflet which accompanies the elec-
trode and the 8.109.1476 Manual of Ion-sensitive Electrodes.
4. pH/Ion Meter
If the pH/Ion Meter is thought to be the cause of a measuring prob-
lem then first check all the configuration and parameter settings.
The diagnostic functions help you in searching for the fault (see
Section 8.5).
The pH/Ion Meter will inform you directly about problems during the
measurement. These messages are explained in the following Sec-
tion 8.2.
A further possibility of carrying out a selective search for a pH electrode
fault is the electrode test. This is described in Section 8.6, where you
will also find specific measures for remedying any fault discovered dur-
ing the test.
The following table lists general problems that can occur during pH and
ISE measurements. Possible causes and appropriate remedies are also
described.