The ammonium ions contained in the sample are converted into ammonia through the addition of NaOH. The ammonia then diffuses through a gas-permeable membrane and is detected by means of a combined pH electrode. Depending on the application, Metrohm offers a choice of two versions.
For measurements in waters with low concentrations of ammonium (e.g. drinking water, boiler feed water, etc.), the NH3-ISE (Low) version with preassembled, individually tested and certified complete modules is recommended. The membranes used in this version are characterized by a faster response time and lower detection limit.
The demands on devices used for measurements in highly polluted samples (e.g. wastewater containing oil residues) are correspondingly higher. For these, Metrohm offers the NH3-ISE (High), the version in which only the membrane needs to be replaced at regular intervals. The type of membrane used in this version is characterized by shorter regeneration times and better signal stability at high ammonium concentrations.