PVC MEMBRANE ELECTRODES FOR MANUAL AND FLOW-INJECTION DETERMINATION OF TETRAPHENYLBORATE - APPLICATIONS TO SEPARATE AND SEQUENTIAL TITRATIONS OF SOME METAL-IONS

Three novel poly (vinyl chloride) matrix membrane electrodes, highly sensitive and selective for tetraphenylborate anion (TPB), are developed and electrochemically evaluated. They are based on the use of iron(II) bathophenanthroline, nickel(II) bathophenanthroline-and nitron-TPB ion-pair complexes as electroactive materials with dioctylphthalate (DOP) and 2-nitrophenyl phenyl ether (NPPE) as plasticizing solvent mediators. The electrodes exhibit stable and rapid near-Nernstian response for 10(-2)-10(-6) M TPB over the pH range 4-10. Use of these electrodes for direct potentiometric determination and potentiometric titration of as low as 1 mug of TPB/ml and 0.6 mg of TPB/ml give results with average recoveries of 99.3% (mean standard deviation 0.5%) and 99.4% (mean standard deviation 0.2%), respectively. Incorporation of nitron-TPB PVC sensor in a flow-through sandwich cell provides an efficient flow-injection detector for determining TPB with an input rate of at least 60 samples/hr. The limit of detection is 1.6 mug TPB/nil in a 20-mul sample. The electrodes am also used to monitor separate and sequential titrations of some metal ions with TPB. Alkaline earth and transition-metal ions upon reaction with polyethylene glycol and ethylenediamine, respectively, form cationic complexes readily titrated with TPB. Optimum conditions are outlined for sequential titrations of various combinations of metallic species.