Titrimetric determination of potassium in river water using solvent extraction

Hexyl-H (2, 4, 6, 2', 4', 6'-Hexanitrodiphenylamine) reacts with potassium ion to form water-insoluble precipitate which can be extracted into nitrobenzene. This has been applied to the determination of potassium in river water. Potassium in aqueous phase (2.5×10-5M, 500ml) is extracted into nitrobenzene (50ml) containing Hexyl-Na, the concentration of which is 0.02M. Then the organic phase (40ml) is shaken with 10ml of hydrochloric acid (pH =1). In these procedures, potassium is enriched as forty times that in the initial solution. The back-extracted potassium is precipitated with an excess of TPB-Na (sodium tetraphenylborate), and after filtration the excess of the reagent is back-titrated with a quarternary ammonium salts (tetradecyldimethylbenzylammonium chloride), Titan Yellow being used as an indicator. In this titrimetry, potassium, such as 0.7×10-32×10-3M, could be determined within an error of ±0.04×10-3M. By using the above-mentioned procedure, potassium, such as 2×10-55×10-5M, was determined within ±4% in the relative error. This method could be applied satisfactorily to the determination of potassium in river water and tap water.