Sensitive determination and electrochemical evaluation of anticancer drug tofacitinib in pharmaceutical and biological samples using glassy carbon and boron-doped diamond electrodes

In 2012, the Food and Drug Administration (FDA, USA) approved tofacitinib citrate (TOF), a Janus kinase (JAK) inhibitor, for the treatment of individuals with moderate-to-severe rheumatoid arthritis (RA). For the determination of TOF, sensitive, fast, and environmentally friendly electroanalytical methods were developed for the first time using glassy carbon electrode (GCE) and boron-doped diamond electrode (BDDE). The effects of pH, supporting electrolyte, and scanning rate on TOF's peak current and potentials were investigated in detail using both electrodes. Irreversible anodic peaks were obtained at pH 4.7 acetate buffer and pH 8.0 phosphate buffer media using cyclic voltammetry at 0.65 V and 0.55 V for GCE and 0.74 V and 0.66 V for BDDE, respectively. Furthermore, the electrochemical oxidation process of TOF was determined by cyclic voltammetry (CV). The results were found to be diffusion-controlled and irreversible at both electrodes. In addition, the mechanism of the oxidation process was investigated using model compounds. Under optimized conditions, low detection limits of 2.75 x 10-7 and 5.22 x 10-8 M were obtained for the electrochemical signal of the electrodes, GCE and BDDE, respectively. Also, the linear concentration ranges were found between 2.0 x 10-6 M and 1.0 x 10-4 M for GCE and 1.0 x 10-6 M and 1.0 x 10-4 M for BDDE. These proposed methods were applied to determine the amount of TOF in pharmaceutical dosage forms and serum samples with excellent recovery results.