Development of potentiometric sensors based on thiourea derivatives, Gd2O3@rGO and MoO3@rGO for the determination of salicylate in drug tablets and biofluids and DFT studies

Abstract

Determination of salicylates in pharmaceutical formulations and biofluids is of great importance because of the toxicity of high doses in the blood. However, most analytical methods used for salicylate determination are expensive and time-consuming. In this study, potentiometric sensors based on carbon paste electrodes (CPEs) with the thiourea derivative (TUD1, ionophore) were successfully constructed for the detection of salicylate levels in pharmaceutical formulations and biofluids. Computational studies at the density functional theory (DFT) level were utilized to estimate inter-and intra-molecular interactions between salicylate and TUD1. The sensitivity of the CPEs to salicylate ions was optimized using different plasticizers (2-nitrophenyloctyl ether-NPOE, tricresyl phosphate-TCP, and dibutyl phthalate-DPB), nanomaterials (Gd2O3@rGO and MoO3@rGO), and ion exchanger (tridodecylmethylammonium chloride-TDMAC). The use of nanomaterials (Gd2O3@rGO and MoO3@rGO) improved the sensitivity and response time of the sensor over a wide pH range (4–10). The best sensor achieved a Nernst slope of 60 mV/decade over a dynamic concentration of 10−5 to 10−1 M with a detection limit of 10−5 M and good selectivity to interfering ions (Cl−, F−, Br−, benzoate, uric acid, and ascorbic acid) compared to previous reports. In addition, the sensor exhibited a lifetime of 6 months without any significant change in sensitivity (less than 5 % deviation). The developed sensors were successfully used for the determination of salicylate in tablets (Aspocid®), spiked serum, and spiked urine with high accuracy.