BENZOATE ION-SELECTIVE ELECTRODE WITH IMPROVED SELECTIVITY AND REPRODUCIBILITY FOR BENZOATE DETERMINATION IN MEDICINAL SYRUPS

This paper describes the construction and evaluation of a benzoate ani on selective electrode with enhanced working characteristics, namely r eproducibility and selectivity, to be used in medicinal syrups analysi s by direct potentiometry. The electrode, without an internal referenc e solution, was prepared with a PVC membrane, based on bis(triphenylph osphoranylidene) ammonium benzoate as ion-exchanger, dissolved in 2-ni trophenyl octyl ether as mediator solvent and 4-t-octylphenol as addit ive. The characteristics of the electrodes were evaluated in sodium be nzoate solutions with adjusted ionic strength and showed a linear resp onse in the range 10(-2)-2 x 10(-4) mol dm(-3) with a slope of 54.7 +/ - 0.5 mV/decade and a reproducibility of +/- 0.2 mV/day for solutions with pH 6.3. The potentiometric selectivity coefficients were determin ed for some possible interfering species and showed that the electrode s prepared with the additive had good selectivity, especially over iod ide and nitrate, when compared with those without any additive. The el ectrodes were used for benzoate determinations in several medicinal sy rups by direct potentiometry. The results gave recovery values in the range 98.3-104.6%.