Application of a new potentiometric method for determination of phosphate based on a surfactant-modified zeolite carbon-paste electrode (SMZ-CPE).

A phosphate-selective electrode based on surfactant-modified zeolite (SMZ) particles into carbon-paste has been proposed (SMZ-CPE). The electrode was fully characterized in terms of composition, response time, ionic strength, thermal stability and usable pH range. The electrode containing 20% SMZ exhibited linear response range to phosphate species in the range of 1.58 x 10(-5) to 1.00 x 10(-2) M with a detection limit of 1.28 x 10(-5) M and a Nernstian slope of 29.9+/-0.9 mV per decade of phosphate concentration. The electrode response to phosphate remains constant in the pH range of 4-12 and in the presence of 1 x 10(-4) to 4 x 10(-3) M NaNO(3). The response of the electrode reaches equilibrium within several seconds after immersing the electrode in phosphate solution. Common anions such as Cl(-), Br(-), I(-), NO(3)(-), SO(4)(2-) and Cr(2)O(7)(2-) have little effect on the determination of phosphate but AsO(4)(3-) shows some interference. A successful application of the electrode for determination of phosphate in a fertilizer, using direct potentiometry, is presented. The electrode was also used for the potentiometric titration of phosphate. The validation of the obtained results in each case was proved by statistical methods. Copyright 2009 Elsevier B.V. All rights reserved.