Metrohm 781 pH/Ion Meter - Manual (Page 142)

8.6 pH electrode test
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780/781 pH/Ion Meter, Manual
Test criterion Message Measure
pH 9: absolute drift in stirred
solution > 1 mV/min
problem Clean diaphragm and/or
regenerate the glass membrane.
pH 9:
-10 mV < U(unstirred) < 10 mV
AND
sum of abs. drift values after 1, 2,
3 and 4 min < 12 mV/min
short circuit Replace electrode (short circuit
or crack in glass membrane).
2 slopes do not meet the
conditions for a passing
electrode
check buffer/
electrode Repeat test using correct
buffers.
Electrode poor as streaming
potential dU is too high
bad diaphragm Clean diaphragm.
All slopes meet conditions for
passing electrode
AND
Uoff outside the preset limit
reference not
matching Repeat with suitable reference
system; replace contaminated
reference electrolyte. If
necessary select electrode type
' own ' and adapt the Uoff limits.
All slopes do not meet conditions
for passing electrode
partial short
circuit Check temperature sensor or
enter correct temperature. If this
does not help then replace pH
electrode.
A response time does not meet
the criterion for passing electrode
glass
membrane/
reference Regenerate glass membrane
and/or clean diaphragm.
8.6.5 Care and maintenance of pH glass electrodes
General
• A combined pH electrode must be filled with the correct refer-
ence electrolyte, e.g. with c(KCl) = 3 mol/L.
• The reference electrolyte chamber should be completely filled
with clean electrolyte.
• The reference electrolyte filling opening must remain open during
the measurement and be closed during storage.
• There should be no air bubbles in the inner or reference electro-
lyte.
• All cable connections should be clean and dry.