Bi-component sensing platform for the detection of Cd²⁺, Fe²⁺and Fe³⁺ ions

The ability of N-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)isonicotinamide (naphydrazide) or 2,6-pyridinedicarboxylic acid (2,6-H₂pdc) individually or as a bi-component system in distinguishing and detecting Fe³⁺ or Fe²⁺ and Cd²⁺ ions was investigated. The use of these molecules as single or bi-component analytes in absorption or emission spectroscopy studies showed that under specific conditions each had their own merits for specific purposes. UV-visible spectroscopic studies of 2,6-H₂pdc for assessing the interactions with ferrous and ferric ions showed characteristic distinctions. The detection limit for Fe³⁺ analysed through UV-visible spectroscopy using naphydrazide was 0.46 μM, whereas it was 1.28 μM using 2,6-H₂pdc. Naphydrazide together with Fe³⁺ allowed distinguishing Cd²⁺ ions from Zn²⁺ and Fe²⁺ ions. The bi-component system was useful for the selective detection of Cd²⁺ ions using fluorescence spectroscopy, with a detection limit for Cd²⁺ ions of 18.31 μM. The presence of Fe²⁺ and Cd²⁺ ions in a solution of the bi-component had resulted white-light emission. An analogous compound N,N'-(1,3,6,8-tetraoxobenzo[lmn][3,8]phenanthroline-2,7(1H,3H,6H,8H)-diyl)diisonicotinamide (binaphydrazide) was found unsuitable for such detections. Two 2,6-pyridinedicarboxylate Fe³⁺ complexes possessing protonated naphydrazide or binaphydrazide were prepared and characterised. These complexes were also found unsuitable for the detection of the said ions in solution. Electrochemical studies with the bi-component system showed that cyclic voltammograms could distinguish Fe³⁺ or Fe²⁺ from Cd²⁺ ions.