This method is for determining the concentration of ammonium ionin aqueous solutions by Ion Chromatography (IC). The limit ofquantitation of the method is 0.0001 mass-% (1 mass-ppm). Sodiumand potassium interfere with the analysis when they are present atconcentrations greater than 0.1 mass-%. Acidic samples that containgreater than 50-mM hydronium ion concentration (pH less than 1.3)deteriorate the performance of the analysis (through loss ofresolution). Organic contamination should also be kept to a minimum(to lengthen column life). Sample matrix effects can be avoided orminimized by sample dilution, but only at the expense of theanalysis limit of quantitation. When used in conjunction with UOPMethod 958 (an extraction procedure), ammonia can also bedetermined in hydrocarbon samples.