Thermo Fisher Scientific Ion Selective Electrodes Ammonia - Manual (Page 22)

value correctly
incorrect standards prepare fresh standards
wrong units used apply correct conversion factor:
10-
3
M = 17 ppm as
NH
3
= 14 ppm as N
buffer added to add same proportions of buffer to
standards and not standards and samples
samples
sample carryover rinse electrodes thoroughly
between samples
Checking the Electrode Inner Body
If the electrode slope is found to be low during operation, the following solutions will be necessary
to check the inner body:
- pH 4 Buffer (0.1M NaCl added)
Add 2.9 grams of reagent-grade NaCl to 500 ml of pH 4 buffer. Dissolve the solid. The solution
may be stored for repeated use.
- pH 7 Buffer (0.1M NaCl added)
Add 2.9 grams of reagent-grade NaCl to 500 ml of pH 7 buffer. Dissolve the solid. The solution
may be stored for repeated use.
Disassemble the ammonia electrode. If the electrode is dry, soak the glass tip of the inner body in
Eutech Ammonia Electrode Filling Solution (Code No. EC-RE-032) for at least two hours.
Rinse the electrode thoroughly with distilled water. Put 100 ml of pH 7 buffer (0.1M NaCl added)
in a 150 ml beaker. Place the beaker on the magnetic stirrer, and begin stirring. Immerse the tip of
the inner body in the solution so that the reference element is covered. Make sure that the meter is
in the mV mode. Record the meter reading when stable.
Rinse the inner body thoroughly in distilled water. Put 100 ml of pH 4 buffer (0.1M NaCl added) in
a 150 ml beaker, place the beaker on the magnetic stirrer, and begin stirring. Immerse the tip of the
inner body in the solution so that the reference element is covered. Observe the change in the meter
reading carefully. In less than 30 seconds after immersion, the reading should change 100 mV. The
meter reading should stabilize in 3 - 4 minutes, with a difference greater than 150 mV if the inner
body sensing elements are operating properly.