Coated-Carbon Rod Ion-Selective Electrode for the Determination of Niobium in Citric Medium

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Abstract
The construction and analytical evaluation of a coated-graph i te niobium ion-selective electrode, based on the ion-pair-between [NbO(Citr)2]3− anion and tricaprylylmethylanunoni um cation (Aliquat 336S) in poly (vinylchloride) matrix, are described. The influence of membrane composition, organic acid concentration and foreign ions were investigated. The electrode shows a Nernstian response over the niobium concentration range 2.0 × 10−5 − 7.9 × 10−3 M, with good selectivity, precision and a useful lifetime of six months (over 800 determinations) in citric acid. Application of this sensor for niobium determination in columbite is reported.