Use of cobalt(ii) and chromium(iii) metal-based Schiff base complexes for the preparation of potentiometric sensors to determine bromide at ultra-low concentrations

Abstract

Co(II) and Cr(III) salicylidene Schiff base-based complexes as novel ionophores were evaluated for the fabrication of bromide-selective electrodes. By incorporating a cation excluder along with various plasticizers (dibutyl phthalate, dioctyl phthalate, 1-chloronapthalene), optimized sensors (CoC7 and CrC7) exhibiting near-Nernstian slopes being 59.4 ± 0.07 and 59.2 ± 0.04 mV decade⁻¹, with a broad linear range (1 × 10⁻² to 6.0 × 10⁻⁷ and 1 × 10⁻² to 8.7 × 10⁻⁷ mol L⁻¹), with low detection limits (5.5 ± 0.13 × 10⁻⁷ and 6.5 ± 0.07 × 10⁻⁷ mol L⁻¹) respectively, were successfully designed. Selectivity coefficient values of order 10⁻¹ or less indicate that the proposed electrodes have superior selectivity for bromide ions over various interfering anions. The developed bromide electrodes demonstrated robust performance within a pH range of 4.0 to 9.0, as well as showing a sufficient shelf life (4 and 5 weeks) with up to 20% (v/v) non-aqueous tolerance and quick response times (12 and 16 s). These electrodes also served as indicator electrodes in the potentiometric titration of bromide ions against AgNO₃ and were used in the determination of bromide ion concentration in water samples.