Synthesis of chloride ion-selective potentiometric sensor based on coordination polymer complex

Abstract

This paper describes the fabrication of an ion-selective electrode in which a 2,5-dihydroxy-p-benzoquinone (DHBQ) is used as the ionophore. The polymers prepared were characterized by elemental analyses, FT-infrared spectra, solid state electrical conductivity studies leading to activation energy, conductance measurements and thermoelectric power measurements. The DC conductance (1/R) values of Fe(III)-DHBQ, Co(II)-DHBQ, Ni(II)-DHBQ and Cu(II)-DHBQ are 8.75x10⁻⁸, 11.8x10⁻⁸, 8.33x10⁻⁸ and 1.28x10⁻⁸ Ω⁻¹, respectively. The current increase exponentially against temperature proves the semiconductive nature. Thermoelectric power (TEP) measurements showed the sign of the seebeck coefficient which was positive in the temperature range and hence it was concluded that the majority carriers are of n-type. The low activation energy is interpreted in terms of intermediate trap levels. The main advantage of the electrode is that it is mechanically stable up to 3 years. The electrode shows a linear response in the range of 2.5 x 10⁻⁵ – 0.5 x 10⁻¹ mol dm⁻³. The response time of the electrode is 30 s. The pH range at which the electrode works is 3.8 to 6.8. The electrode was found to be selective towards chloride ion in the presence of ions like Na⁺, Ca²⁺, Mn²⁺, Fe³⁺, Co²⁺, Cu²⁺, Zn²⁺, CH₃COO⁻, NO₃⁻, SO₄²⁻, Br⁻ and NO₂⁻.