The standard applies to all types of water in boiler operations with a sulphate content of at least 10 mg/l. If more than 5 mg phosphate, 5 mg nitrate, 50 mg calcium, or 50 mg iron are present in the analysis sample, the determination is impaired. Notes 1. For water samples containing more silica than 5 (m/m) % of the expected sulphate content, the removal of silica is described in a separate method. 2. If more than 5 mg nitrate is present in the analysis sample, this must be removed by evaporation with hydrochloric acid. 3. Interference with the determination due to the presence of more than 50 mg calcium and/or more than 50 mg iron in the analysis sample is remedied by adding EDTA. However, this method results in higher blank values, which increases the lower analytical limit of the determination.
NEN 6544-1990 history
1990NEN 6544-1990 Water for boiler plants Gravimetricdetermination of sulfate content