Optical ligand–thorium complex sensors using various reagents and the comparison of formation constants obtained in dip probe, flow cell and microchip systems

Thorium is an important element not only from an environmental perspective but also in industrial applications. In this study, Arsenazo III, Thorin and Thionin were used as complexation reagents for the determination of Thorium using flow cell, dip probe and microchip systems [P. Caglar, S.A. Tuncel, N. Malcik, J.P. Landers, J. Ferrance, A microchip sensor for calcium determination, Anal. Bioanal. Chem. 386 (2006) 1303–1312]. For this aim, the spectral characteristics of Th4+–dye complexes, and the effects of pH on the formation of Th4+–Ars III, Th4+–Thorin and Th4+–Thionin complexes have been determined. The determination of the complex stoichiometries and the complex formation constants were also studied using the three systems. The complex stoichiometries were found to be 1:1 for all ligands and for all systems under study in this paper. Nevertheless, the formation constants (Kf) have been determined as 2.340 × 106, 8.156 × 105, and 6.732 × 105 mol L−1 for Th4+–Ars III, Th4+–Thorin and Th4+–Thionin complexes, respectively, using the dip probe system. The Kf values were found to be 9.422 × 104, 6.752 × 104, and 4.199 × 104 mol L−1 for Th4+–Ars III, Th4+–Thorin and Th4+–Thionin complexes, respectively, for the flow cell system, whereas these values were determined as 8.526 × 104, 5.988 × 104, and 3.892 × 104 mol L−1 for Th4+–Ars III, Th4+–Thorin and Th4+–Thionin complexes, respectively, using the microchip system. The response times of the sensors, the linear range of the sensor response, the detection limits and the relative standard deviation (RSD) of the sensors have also been found.