Development of a Composite Cu(II)-Selective Potentiometric Sensor Based on a Thiourea Derivative Symmetric Schiff Base

Abstract. In the present study, initially, a thiourea derivative symmetric Schiff base, (1E,3E)-1,3-bis(5-bromo-2-hydroxybenzylidene)thiourea, was synthesized and characterized by FTIR and SEM-EDX analysis. In addition, an all-solid-state composite Cu(II)-selective potentiometric sensor based on this synthesized compound as an electroactive substance was constructed. Optimization studies indicated that the composition of the optimum sensing composite exhibiting the best potentiometric characteristics was 3.0% Schiff base, 5.0 % multi-walled carbon nanotube (MWCNT), 20.0 % paraffin oil and 72.0% graphite by mass. The proposed sensor displayed a linear response in the concentration range of 5.0×10-6-1.0×10-1 M with a slope of 31.1 mV/decade and a detection limit of 5.0×10-7 M. The proposed sensor exhibited a fairly selective, stable (potential drift: 1.85 mV/h), and rapid (<10 s) response towards Cu(II) ions. Because of the magnitude of its potential drift, the sensor should be recalibrated along the analysis time at least half an hour apart. The sensor can employed safely in the samples with pHs in the range of 2.0-6.5. The lifetime of the fresh sensor surface was determined as 2 weeks. The most important advantage of the sensor is that the sensing composite surface is renewable (at least 10 times) and thus the sensor can be used many times for a long period of time. The analytical applications of the sensor were executed successfully by using the electrode in the potentiometric titration of Cu(II) ions with EDTA as an indicator electrode, in the direct determination of Cu(II) contents of spiked water samples, and in the determination of (w/w) Cu% content of a Turkish coin.