This method describes how to determine the sulfate content in water by cation exchange.
Water intended for use as an ingredient in the production of beer (brewing liquor) or other foods
Determining sulfate ions in water is important for evaluating its capacity to attack concrete and mortar. The concentration of sulfate ions has an impact on the choice of treatment techniques and therefore on the chemicals used for boiler feed water and for coolants. In brewing liquor, it can affect the character of the beer.
A water sample is run through an ion exchanger in which all of the cations are replaced with hydrogen ions. The sulfate is determined through titration in the presence of a previously prepared barium chloride solution, of which a known amount in excess of that required is added in advance. The quantity is measured by complexometric titration. The difference between the initial concentration of barium chloride and the amount determined by back titration corresponds to the sulfate content.
In many cases, particularly at higher contents, an alternative and sufficiently accurate measurement is possible, called the “negative m value” or the “total mineral acid value” (without carbonic acid). This is achieved through titration. Subsequently, the mval values for the anions (Cl-, NO3-, NO2-, PO43-) are subtracted from the result.