Utilization of a plasticized PVC optical sensor for the selective and efficient detection of cobalt(ii) in...

A novel sensitive, selective, and reversible cobalt(ii) ion optical sensor was prepared by the incorporation of 5-[o-carboxyphenylazo]2,4-dihydroxybenzoic acid [CPDB] and sodium tetraphenylborate (NaTPB) in a plasticized polyvinyl chloride (PVC) membrane containing dioctyl adipate (DOA) as a plasticizer. The influence of several parameters such as pH, base matrix, solvent mediator and reagent concentration was optimized. A comparison of the obtained results with those of previously reported sensors revealed that the proposed method, in addition to being fast and simple, provided a good linear range (0.05-45.20 μM) and low detection limit (0.015 μM). Low detection and quantification limits and excellent selectivity in the presence of interfering ions such as Fe³⁺, Cu²⁺, Ni²⁺, Ag⁺, Au³⁺, Cr³⁺, Cd²⁺, Zn²⁺, Hg²⁺, and SO₄ ^2- make it feasible to monitor Co²⁺ ion content accurately and repeatedly in environmental samples with complicated matrices. The optode was regenerated successfully using 0.3 M nitric acid (HNO₃) solution while its response was reversible with a relative standard deviation (RSD) lower than 1.9% for seven replicate determinations of 20 μM Co²⁺ in various membranes. The optode was stable and was stored for at least 15 days without observing any change in its sensitivity.