Highly Selective Detection of Titanium (III) in Industrial Waste Water Samples Using Meso-octamethylcalix[4]pyrrole-Doped PVC Membrane Ion-Selective Electrode

Abstract A novel Ti 3+ selective membrane electrode based on meso-octamethylcalix[4]pyrrole (OMCP) as an ionophore was successfully fabricated. The developed sensor revealed high selectivity towards Ti 3+ ion over alkali, alkaline earth and transition metal cations. Among all of the membranes examined, the membrane with a composition of 4:33:62.8:0.2 mg of I:PVC:DOP:NaTFPB showed the best Nernstian slope of 29.49 ± 0.16 (mV per decade of activity) over the pH range from 1 to 3 with a satisfactory concentration range of 1.0 × 10 −6  M to 1.0 × 10 −2  M and detection limit of 8.0 × 10 −7  M. The effects of various parameters such as composition of the membrane, different cation interferences and concentration of internal solution were investigated. The developed sensor exhibited a good reproducibility over a useful life time of about 3 months with a fast response time of 25 seconds. It demonstrated good analytical performance for accurate determination of Ti 3+ trace amount in the presence of considerable concentration of common interfering ions. The fabricated sensor was used successfully as an indicator electrode for potentiometric titration of a titanium solution with EDTA and moreover it applied for direct determination of Ti 3+ content of industrial waste water samples. The obtained results from optimized membranes were evaluated by comparing them with the data received from instrumental methods such as UV–Vis, AAS, ICP and SEM. By using density functional theory (DFT) calculations, several special adsorption sites of TiOH 2+ close to OMCP are fully optimized and the best one selected. Furthermore, NBO and QTAIM analysis carried out to study the bonding strength in formed complex and deep understanding of the nature of interaction between TiOH 2+ and OMCP.