The common alkali and alkaline earth cations are not considered primary drinking water contaminants in the U.S. However, they are monitored and reported by many U.S. public water suppliers, and are regulated in the EU and Japan. Calcium and magnesium are also routinely measured to determine water hardness, an important metric for corrosion control. Ammonia is a colorless, pungent gas. It is highly soluble in water, where it exists in equilibrium between a molecular form associated with water and the ionized form (the ammonium cation, NH 4+). The extent of its toxicity to aquatic life depends on the extent of dissociation, which in turn depends on temperature and pH. Ammonia can enter environmental waters as a product of anaerobic decomposition of nitrogen containing compounds or from waste streams containing ammonia. Ammonium cation is routinely measured in the U.S. for wastewater discharge compliance monitoring, and in the EU and Japan in both wastewater and drinking water. Alkali and alkaline earth cations are commonly determined using spectroscopic techniques such as AAS or ICP, but ammonium cation in the same sample must be measured separately by a wet chemical technique (such as titrimetry, colorimetry, Nesslerization, phenate, or automated phenate methods), or an ammonia selective electrode. Furthermore, the latter two methods may also require a separate distillation step before ammonia can be determined in wastewater. Ion chromatography (IC) can, in a single run, determine ammonium and all the important inorganic cations, including lithium, sodium, potassium, magnesium, and calcium. 
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