Metrohm NH3-selective electrodes - Manual (Page 20)

7.1 Problems and their solutions
￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭
14 ￭￭￭￭￭￭￭￭
NH
3
-selective electrodes
7 Troubleshooting
7.1 Problems and their solutions
Problem Cause Remedy
The electrode slope
is too large (> 62
mV). The electrode was insuffi-
ciently prepared or condi-
tioned for too short a time
in distilled water. Refill the electrode and condition for at least
30 minutes in distilled water.
The electrode slope
is too small. The membrane has a tear. Replace the membrane or the membrane
module.
The calibration solutions
are contaminated or they
have been used too long. Use fresh calibration solutions.
Either too little sodium
hydroxide solution was
added, or none at all. Add 1 mL sodium hydroxide solution with
c(NaOH) = 10 mol/L per 100 mL measuring
solution.
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 measuring electrode
was in dry storage. Soak the measuring electrode for 6 to 12
hours in pH 7 buffer solution.
The measuring
range is exceeded. The measuring device is
possibly defective. Check the measuring device.
The electrode is not con-
nected correctly. Check the electrode connection.
The calibration is no longer
accurate. Recalibrate the electrode.
There is no measuring elec-
trolyte in the membrane
module. Unscrew the membrane module 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