SALICYLATE ION-SELECTIVE MEMBRANE ELECTRO DES BASED ON METAL-BIS(DIPHENYLPHOSPHINO)PROPANE COMPLEXES

The response properties of membrane-coated carbon rod electrodes towar d the salicylate anion were investigated. New electrodes were prepared by incorporating bis-(diphenylphosphino)propane (BDPPP) into a plasti cized poly(vinyl chloride) membrane, and then coating it on a carbon r od surface. These electrodes were used for immersion into a solution c ontaining a metal {Pd(II), Rh(III) or Cu(II)} and salicylate ions in o rder to form BDPPP complexes inside the membrane. Although the two oth er complexes responded to the salicylate ion, the electrode with the C u(II) complex showed the following good response properties: a near-Ne rnstian slope of 58 approximately 60 mV/decade, detection limit of 8 X 10(-6) mol dm-3 and a response time of 5 approximately 6s over a pH r ange of 4.5 approximately 9.5. The order of the selectivity coefficien t for foreign anions roughly followed the Hoffmeister series. The inte rfering effects of acetate and benzoate ions were rather weak, as was the effect of the chloride ion, when compared to that of an electrode based on the tin(IV) porphyrin complex. BDPPP forms a 1 : 2 Cu(II)/lig and complex in which the exchange of counter anion produces the potent ial response.