Voltammetric determination of phosphates using ion-selective electrode based on organotin ionophore

This work describes the development of an amperometric phosphate-selective electrode with a plasticized membrane that includes bis(2-ethylhexyl)tin (IV) dichloride as an ionophore. The potentiometric response of the plasticized membrane was investigated, in addition to its selectivity for hydrophilic anions. The membrane provided a linear potential response with respect to HPO42- ions in the concentration range from 4·10-5 to 3·10-2 mol/L with a Nernst slope of 29 ± 2 mV·decade-1 activity. By using cyclic voltammetry, we characterized the ionophore-facilitated transfer of mono- and dihydro phosphate ions at the water/PVC-2-nitrophenyl octyl ether phase interface. An interphase distribution coefficient, a galvanic potential, a half-wave potential, the Gibbs energy of facilitated interphase transfer, as well as the Gibbs energy of facilitated interphase transfer were determined. Alternating current voltammetry was used to quantify phosphate ions in aqueous solutions. The linear response was observed in the range of phosphate concentrations from 2 to 10-6 to 1·10-4 mol/L and the detection limit was 8·10-7 mol/L under these conditions. This AISE has demonstrated high selectivity for phosphate ions in comparison to the most common anions in aqueous solutions. It has been used to determine the amount of phosphates in two fertilizers.