Abstract
Thiourea derivative-based carbon paste electrode (TUD1-CPE) was constructed as a potentiometric sensor for the determination of salicylate anion in pharmaceutical formulations, Aspocid (R) and Aspirin (R). The optimized CPE contained 45.5 % graphite, 0.5 % reduced graphene oxide (rGO), 46.0 % nitrophenyl octyl ether (NPOE) plasticizer, 5.0 % TUD1 ionophore, and 3.0 % tridodecylmethyl ammonium chloride as additive. The incorporation of NPOE of high dielectric constant, and rGO in electrode caused better performance of the sensor; Nernstian response of 59.0 mV decade(-1) in the concentration range of 10(-1)-10(-5) mole L-1, a detection limit of 1x10(-5) mole L-1 in a very short response time of 6 seconds. The prepared sensor showed high selectivity against similar anions (i. e. ClO4-, benzoate, I-, SCN-). Selectivity was confirmed by calculating the formation constant (K-beta) using sandwich membrane method, where K-beta for TUD1-salicylate is 10(0.43). Theoretical calculations at DFT-B3LY/6-31G** level of theory were performed to find interaction mechanism, Energies of HOMO and LUMO orbitals, non-linear optical (NLO) properties (the electronic dipole moment (mu), first-order hyperpolarizability (beta), the hyper-Rayleigh scattering (beta(HRS)) and the depolarization ratio (DR)), and other global properties; these calculations showed lower values of beta and DR, higher value of beta(HRS), and the shortest lengths of the four N-H bonds between TUD1 and salicylate which confirm their strong complexation and salicylate-selectivity. Also, all the studied anion-TUD1 exhibited relatively high NLO properties, and these results were considered as a preliminary study for investigating new types of NLO bearing materials. The sensors were applied successfully for the determination of salicylate anion in Aspocid (R) and Aspirin (R).