Potentiometric Sensing of Aspirin Metabolite in Human Plasma and Pharmaceutical Preparations Using Co(III)-complex Based Electrodes: Experimental and Quantum Chemical Calculations

Three novel poly vinyl chloride (PVC) (A), carbon paste (CP) (B), and coated glassy carbon-MWCNT (CGC) (C) salicylate (sal^-) sensors based on new synthesized [Co(L^2Cl)Cl₃(H₂O)](dot operator)H₂O complex (L^2Cl=(1H-benzimidazol-2-ylmethyl)-N-(2-chloro-phenyl)- amine)), o-nitrophenyloctyl ether as a mediator and tridodecylmethylammonium chloride as a cationic additive were successfully used for determination of sal^- in human plasma and pharmaceutical formulations. The sal^--sensors exhibited enhanced sensitivity with slope of -63.5, -60.5 and -58.9mV/decade and detection limit of 1.0×10^-5, 4.0×10^-7, and 1.0×10^-6molL^-1 for A-C sensors respectively. Quantum chemical calculations were carried out by HF and DFT/B3LYP methods to explore and investigate the interaction between the receptor and the different anions. The intermolecular H-bond created between the uncoordinated C=O of salicylate group and the secondary amino group in the complex is the key factor of the selectivity of the proposed sensor. A linear relation is established between the natural charge on the Co center and the value of the binding energy, where the decrease in positive charge is associated by an increase in the anion binding energy.