Determination of ammonium is one of the most crucial applications for sectors such as water and wastewater analysis, fertilizers, and others. Metrohm Application Bulletin AB-133 describes the determination of Ammonium by ion measurement according to ISO 6778, EPA 359.2, EPA 305.3, and ASTM D1426. Tips & Tricks on how on how to deal with possible interferences, sample preparation, and handling of the ammonia ion selective electrode are also covered.