Direct analysis of thorium(IV) ions concentration in water samples using a new carbon paste electrode.

The radioactive and hazardous nature of thorium demands the fabrication of efficient electrodes for its sensitive and selective monitoring in aqueous environments. The present paper reports the construction and characterization of a new carbon paste electrode (CPE) chemically modified by octyl phenyl acid phosphate (OPAP) as a selective recognition agent for the potentiometric assay of thorium(IV) ions. Improved sensitivity, electrical conductivity, and selectivity were achieved by incorporating oxidized multi-walled carbon nanotubes (o-MWCNTs) into the carbon paste composition. The electrochemical performance of the developed electrode was evaluated regarding the paste ingredients, response time, and working pH range. The standard CPE potentials, E°, were determined at various temperatures and the isothermal temperature coefficient was calculated. The optimized CPE showed a Nernstian slope of 14.65 ± 0.38 mV decade−1 over the concentration range of 4.82 × 10–7–1.00 × 10–1 mol L−1. The electrode possessed a short response time (9 s), independence of the solution pH over the range of 2.5–5.5, and a relatively long operational lifetime (˃ 3 months). The selectivity coefficients indicated the good discrimination ability of the developed CPE towards thorium(IV) ion compared to various common ions. Aiming to judge the practical utility of the developed CPE, it was successfully used for the potentiometric analysis of thorium(IV) ions in various real aqueous matrices with sensible results. [ABSTRACT FROM AUTHOR]