ISO 5310:1986 Fertilizers - Determination of potassium content - Titrimetric method Engrais

This International Standard specifies a titrimetric method for the determination of the potassium content of fertilizers.
Preparation of a test Solution as specified in ISO 5317 or ISO 7407. Precipitation of potassium ions present in an aliquot Portion of the test Solution (previously treated with bromine water and activated charcoal if cyanamide and/or organic materials are present) by an excess of sodium etraphenylborate (NaTPB) in a weakly alkaline medium. Filtration and determination of the unused NaTPB by back titration with etyltrimethylammonium bromide solution, using thiazol yellow as indicator.