POLY(VINYL CHLORIDE) MATRIX MEMBRANE ELECTRODES FOR THE SELECTIVE DETERMINATION OF BUFORMIN

Two poly(vinyl chloride) matrix membrane buformin-selective electrodes have been developed, for the direct determination of the buformin cation in aqueous solutions. These membrane electrodes are based on the use of ion-association complexes of the buformin hydrochloride cation with either tetraphenylborate (I) or 5-nitrobarbiturate (II) counter ions as ion-exchange sites. These electrodes show good selectivity for buformin hydrochloride over wide pH ranges (pH 4-9.5 for electrode I and pH 4-10 for electrode II) in the presence of some inorganic as well as organic cations. The two electrode systems exhibit a fast, stable Nernstian response in the ranges 10(-1)-10(-4) mol l(-1) and 10(-1)-10(-5) mol l(-1) for I and II, respectively. The direct potentiometric determinations of buformin hydrochloride in aqueous solutions using electrodes I and II at concentration levels as low as 38.7 or 5.2 mu g ml(-1), respectively, were found to be accurate. The membranes withstood storage for up to 3 months in the dry state.