Titrations of bivalent metal ions with sodium tetraphenylborate in the presence of polyethylene glycol

Abstract

A method is described for the determination of bivalent metal ions with sodium tetraphenylborate, based on the precipitation of ternary compounds in the presence of polyethylene glycol. Titrations of barium(II), lead(II) and strontium(II), in addition to titrations of some mixed systems, have been monitored potentiometrically with a PVC membrane coated-wire electrode plasticised with 2,4-dinitrophenyl octyl ether. The value of the potentiometric titration break depends on the ionic radius of the ion determined and follows the sequence Ba²⁺ > Pb²⁺ > Sr²⁺ > Ca²⁺, Cd²⁺. The breaks in the titrations of calcium(II) and cadmium(II) cannot be used for reliable end-point readings. The same electrode can be used to monitor the titration of mercury(II), although the determination is based on another principle. The titration of lead(II) in the presence of polyethylene glycol can also be followed amperometrically. Some data on the solubilities of the ternary compounds are given.