TROLL 9500 Operator's Manual - Geotech Environmental Equipment

Multi-ParameterWater Quality TROLL ®15 AmmoniumWhat is Ammonium ?Ammonium (NH 4 + ) is the ionized form of ammonia (NH 3). Ammoniaand ammonium are naturally occurring forms of nitrogen, part of thenitrogen cycle. In natural waters they exist in two forms: Dissolvedammonia 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 pHlevels. At a pH of 6.5 almost all ammonia is in the form of ammonium.However, as the pH increases (becomes more basic), ammonium ischanged into harmful ammonia. Ammonium ions are the predominantspecies in most unpolluted natural water systems where the pH istypically less than 9. Even a small amount of ammonia is detrimentalto fish while a moderate amount of ammonium is tolerated. The lethaldose of ammonia for trout is only 0.2 mg/L.Why Measure Ammonium?Major sources of ammonium are wastewater from sewage treatmentplants, and nitrogen in fertilizers which is transformed to ammonium insoil by microorganisms. Ammonia/ammonium can be a key parameterThe Nitrogen Cyclein the assessment of water and wastewater quality. Measurement ofammonium can yield information on the composition and movementof pollutants in groundwater and surface water, landfill leachate, runofffrom agricultural activities, waste concentrations in fisheries, and nutrientlevels in natural water bodies.The Ammonium SensorThe In-Situ sensor is an ion-selective electrode (ISE) that is selectivefor the ammonium ion (NH 4 + ). It is a double-junction combination ISEwith a silver/silver-chloride reference half-cell, PVC sensing membrane,and reference electrolyte gel. It measures the concentration inparts per million of ammonium ion in solution (calculated as nitrogen,ppm as N).Sensor PreparationTo ensure optimum membrane response, the ammonium sensorshould be thoroughly hydrated in an appropriate solution beforecalibration. A good way to do this is to allow the sensor to soak in thesolution you plan to use for the first calibration point (lowest concentration)for at least 15 minutes and up to several days before calibrationand use.• 1.4 ppm N for calibration in the lower range (concentrations lessthan 14 ppm N)• 140 ppm N for calibration in the upper range (concentrations of 14ppm N and up)The sensor kit includes an empty bottle for this purpose.TROLL 9500 Operator’s Manual 1040095110 rev. 007 01/09