Amperometric Method for the Rapid Determination of Tetraphenylborate lon and Its Appiication to the Analysis of Potassium lon

Abstract

Tetraphenylborate ion was titrated in the presence of a neutral supporting electrolyte (such as sodium nitrate) with a silver nitrate solution by short-circuit amperometry using a rotating platinum wire electrode (1000 rpm) as the indicator and a reference SCE electrode. A O.004mol/1 sodium tetraphenylborate s 1ution in the prese ce f o.1 m 111 sodium nitrate was titrated accurately with a coefficient of variation less than O.1%. Surface active agent such as poly (vinyl pyrrolidone), triton X-100 and triton X-405 at the concentration less than O.0160. did not interfere with the titration.
A method for the determination of potassium ion was as follows. An excess of sodium tetraphenylborate solution was added to an aqueous solution of potassium nitrate at about 800C to form the precipitate of potassium tetraphenylborate. After the solution was cooled to room temperature, sodium nitrate (final concentration O.1 mol/1) was added as the supporting electrolyte, and poly(vinyl pyrrolidone) (O. Ol%)to prevent the potassium tetraphenylborate precipitate from reacting with silver ion. Then the residual tetraphenylborate ion was titrated.
This method is applicable to the determination of potassium in sea water. Firstly, the sum of the residual quantity of tetraphenylborate ion added and all of the halide ions were titrated, then all the halide ions were titrated with a silver nitrate solution for another a1iquot of the sample solution in order to estimate the quantity of potassium ions.