Metrohm NH3-selective electrodes - Manual (Page 21)

￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭
7 Troubleshooting
NH
3
-selective electrodes
￭￭￭￭￭￭￭￭ 15
Problem Cause Remedy
Meter, 867 pH Module or a Titrando. Replace
the measuring electrode if required.
The measuring sig-
nal is noisy, the
measured values are
unstable. There is not enough mea-
suring electrolyte in the
membrane module. Unscrew the membrane module, empty it and
refill it with 2 mL measuring electrolyte.
The pH glass electrode
(measuring electrode) is
possibly defective. For the test, calibrate the pH glass electrode
separately in pH buffer solution or perform an
extensive electrode test with 780/781 pH/Ion
Meter, 867 pH Module or a Titrando. Replace
the measuring electrode if required.
The membrane is contami-
nated (e.g. with oleaginous
sample). Replace the membrane or the membrane
module.
A potential drift
occurs. The membrane is defective
(punctured, discolored,
dampened); measuring
electrolyte runs out. Check the membrane module for tears,
replace the membrane or the membrane mod-
ule if necessary.
The wrong measuring elec-
trolyte is in the membrane
module. Fill the membrane module only with the mea-
suring electrolyte supplied.
The membrane is severely
contaminated: not only
gases, but also sample
passes through the mem-
brane. Replace the membrane or the membrane
module.
The total ion concentration
of the sample is > 1 mol/L. Dilute the sample.
Ammonia escapes too
quickly. Use only closed measuring vessels.
Temperature fluctuations
occur. Observe uniform tempering of the sample,
equipping the measuring vessel with a thermo-
stat if necessary.
The measuring electrode
was in dry storage. Soak the measuring electrode for 6 to 12
hours in pH 7 buffer solution.