In-Situ TROLL 9500 Operators Manual - Manual (Page 109)

104
Multi-Parameter
Water Quality TROLL ®
TROLL 9500 Operator’s Manual 0095110 rev. 007 01/09
15 AMMONIUM
WHAT IS AMMONIUM ?
Ammonium (NH
4
+ ) is the ionized form of ammonia (NH
3
). Ammonia
and ammonium are naturally occurring forms of nitrogen, part of the
nitrogen cycle. In natural waters they exist in two forms: Dissolved
ammonia gas (NH
3
) is highly toxic to aquatic life, while ammonium,
the ionized form (NH
4
+ ), is not. Both may be grouped together as
“total ammonia.”
The ammonia/ammonium equilibrium in water is closely related to pH
levels. At a pH of 6.5 almost all ammonia is in the form of ammonium.
However, as the pH increases (becomes more basic), ammonium is
changed into harmful ammonia. Ammonium ions are the predominant
species in most unpolluted natural water systems where the pH is
typically less than 9. Even a small amount of ammonia is detrimental
to fish while a moderate amount of ammonium is tolerated. The lethal
dose of ammonia for trout is only 0.2 mg/L.
WHY MEASURE AMMONIUM?
Major sources of ammonium are wastewater from sewage treatment
plants, and nitrogen in fertilizers which is transformed to ammonium in
soil by microorganisms. Ammonia/ammonium can be a key parameter
in the assessment of water and wastewater quality. Measurement of
ammonium can yield information on the composition and movement
of pollutants in groundwater and surface water, landfill leachate, runoff
from agricultural activities, waste concentrations in fisheries, and nutri-
ent levels in natural water bodies.
THE AMMONIUM SENSOR
The In-Situ sensor is an ion-selective electrode (ISE) that is selective
for the ammonium ion (NH
4
+ ). It is a double-junction combination ISE
with a silver/silver-chloride reference half-cell, PVC sensing mem-
brane, and reference electrolyte gel. It measures the concentration in
parts per million of ammonium ion in solution (calculated as nitrogen,
ppm as N).
SENSOR PREPARATION
To ensure optimum membrane response, the ammonium sensor
should be thoroughly hydrated in an appropriate solution before
calibration. A good way to do this is to allow the sensor to soak in the
solution you plan to use for the first calibration point (lowest concen-
tration) for at least 15 minutes and up to several days before calibra-
tion and use.
s
than 14 ppm N)
s
ppm N and up)
The sensor kit includes an empty bottle for this purpose.
THE NITROGEN CYCLE