Voltammetric determination of tofacitinib with calix[n]arene modified pencil graphite electrodes

Tofacitinib is used in the treatment of various autoimmune diseases, particularly employed in rheumatoid arthritis and psoriasis illnesses. Determining the amount of tofacitinib in order to provide precise control of drug concentration during treatment is of great importance in order to develop a rapid and sensitive method. In this study, voltammetric determination of tofacitinib is performed with pencil graphite electrodes prepared by electrochemically modified with calix[n]arene derivative compounds, and a new method is developed. In electrochemical studies, modified pencil graphite electrode (PGE) is used as working electrode, anhydrous Ag/AgCl electrode as reference electrode and Pt wire electrode as counter electrode. Pencil graphite electrodes are prepared with three different calix[n]arene derivatives (calix[4]arene, calix[6]arene, calix[8]arene). The preparation of the electrodes is carried out by the cyclic voltammetry (CV) method, and the determination of tofacitinib with the prepared electrodes is carried out by the differential pulse voltammetry (DPV) method. The surface characterization of the electrodes and elemental analysis are done by scanning electron microscopy (SEM), and SEM-EDS respectively. Tofasinib experiments are performed in Britton-Robinson buffer solution (10% (v/v) acetonitrile-water). In accordance with the optimization studies, it is determined that the optimum pH value is 4, the number of cycles is 5 and the scanning speed is 100 mV/s. The optimum calix[n]arene concentration is found to be 0.005 M for all three compounds. Experiments are carried out in the presence of ascorbic acid, caffeine and glucose, which may interfere with the determination of tofacitinib, and it is observed that the mentioned compounds did not significantly affect the determination of tofacitinib. With the developed electrodes, within the scope of real sample studies, tablet formulation and tofacitinib determination in urine samples are also carried out. When the results for both samples are evaluated, it is determined that the recovery values are in the range of 98.0-101.5 %. The limit of detection (LOD) is calculated as 0.0275 ppm for calix[4]arene, 0.0212 ppm for calix[6]arene, and 0.0184 ppm for calix[8]arene, respectively.