Solution studies on the binding properties of uranyl ion toward four different recently synthesized benzo-substituted macrocyclic diamides L1-L4 revealed the occurrence of a 1:1 complexation of the ligands with UO22+ ion, with a stability order of L2 > L1 > L4 > L3. Consequently, L2 was used as a suitable neutral ionophore for the preparation of novel polymeric membrane (PME) and coated graphite (CGE) UO22+-selective electrodes. The electrodes exhibit a Nernstian behavior for UO22+ ions over wide concentration ranges (1.0 × 10−6–1.0 × 10−1 M for PME and 1.0 × 10−7–1.0 × 10−1 M for CGE) and very low limits of detection (8.0 × 10−7 M for PME and 7.3 × 10−8 M for CGE). The proposed potentiometric sensors manifest advantages of fast response and, most importantly, good selectivity with respect to many alkali, alkaline earth, transition, and heavy metal ions. The potentiometric responses of the electrodes are independent of the pH of the test solution in the pH range 2.9–3.7. The CGE was used in flow injection potentiometry and resulted in well defined peaks for uranyl ions with stable baseline, excellent reproducibility and very high sampling rate of 170 injections per hour. The proposed FIP system was used for the determination of trace uranyl ions in real and synthetic samples.

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