Metrohm NH3-selective electrodes - Manual (Page 7)

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1 Introduction
NH
3
-selective electrodes
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1 Introduction
The NH
3
-selective gas membrane electrodes are combined electrodes, i.e.
they contain one measuring electrode and one reference electrode.
They enable the rapid, simple, inexpensive and precise determination of
dissolved ammonia (NH
3
) in aqueous systems, e.g. in natural water, sew-
age, boiler feed water, beer, etc.
In addition, the NH
3
-selective gas membrane electrodes can detect the fol-
lowing substances:
￭ Ammonium ions (NH
4
+ ) after their conversion into ammonia
￭ Organic nitrogen (N) after a Kjeldahl digestion
Discolored or turbid samples do not compromise the measurement, which
means that, generally speaking, no pre-distillation is necessary.
The membrane of the NH
3
-selective electrode is gas-permeable and
water-repellent, i.e. water cannot dampen the membrane and cannot per-
meate the pores. In the case of samples that contain surface-active sub-
stances, or in the case of nonaqueous systems, fluid makes its way into
the membrane. This leads to difficulties, e.g. in the case of sewage sam-
ples (detergents) or with nylon or dye samples (nonaqueous systems). An
ammonia determination of such samples should therefore be carried out
by suspending the electrode above the solution instead of immersing it.