The standard applies to all types of water with a total hardness of at least 5 jumol/l (0.01 meq/l), a calcium content of at least 1 mg/l and a magnesium content of at least 1 mg/l. The determination is generally not suitable for wastewater. Note More than 5 mg magnesium ions in the analysis sample interferes with the calcium determination. Other divalent metals that are determined under the conditions of the method and are included in the total hardness, do not generally occur in dis urbing quantities, except in waste water. Large amounts of carbonate and hydrogen carbonate ions (total more than 10meq/l) are dis urbing, but can be removed (see 11.1). More than 1.5 mg of iron ions in the test sample interfere, but this interference can be eliminated (see 11.2). Such an amount of potassium cyanide is added as to prevent the interference caused by a maximum of 0.2 mg copper in the sample for analysis Any small amounts of lead and zinc are not included in this method.
NEN 6441-1979 history
1979NEN 6441-1979 Water -Determination of total hardness and calcium and magnesium content