ISO 5310:1986

Fertilizers — Determination of potassium content — Titrimetric method

The method consists in precipitating of potassium ions by an excess of sodium tetraphenylborate (NaTPB) in a weakly alkaline medium, filtrating and determing of the unused NaTPB by back titration with cetyltrimethylammoniumbromide solution. The test solution shall be prepared as specified in ISO 5317 or ISO 7407.