POTENTIOMETRIC BACK-TITRATION OF SULFATE ION USING A TETRAPHENYLBORATE DERIVATIVE AS A TITRANT AND A TITRANT-SENSITIVE PLASTICIZED POLY(VINYL CHLORIDE) MEMBRANE-ELECTRODE

A potentiometric back-titration method for the determination of sulfat e ions using a plasticized poly(vinyl chloride) membrane electrode wit hout added ion-exchanger is described. A solution of a derivative of t etraphenylborate is used as titrant. The method is based on the ion as sociation between an excess of 2-aminoperimidinium added to the sulfat e containing sample and the tetraphenylborate derivative in the titran t. The titration end-point is detected as a sharp potential change due to an increase in the concentration of the free tetraphenylborate der ivative at the equivalence point. The sharpness of the titration curve at the end-point is compared for two tetraphenylborate derivatives. G ood results are obtained with a solution of sodium tetrakis (4-fluorop henyl) berate.