Electroanalysis and Simultaneous Determination of 6-Thioguanine in the Presence of Uric Acid and Folic Acid Using a Modified Carbon Nanotube Paste Electrode

The present work describes the preparation and characterization of a carbon nanotube paste electrode modified with 2,7-bis(ferrocenyl ethyl)fluoren-9-one (2,7-BF). This electrode showed an efficient catalytic activity for the electro-oxidation of 6-thioguanine (6-TG), which leads to lowering 6-TG overpotential by more than 610 mV. Also, the values of catalytic rate constant (k = 2.7 x 103 mol-1 L s-1), and diffusion coefficient (D = 2.7 x 10-5 cm2 s) were calculated. In 0.1 M phosphate buffer solution of pH 7.0, the oxidation current increased linearly with two concentration intervals of 6-TG, one is 0.06 to 10.0 µmol L-1 and the other is 10.0 to 160.0 µmol L-1. The detection limit (3σ) obtained by differential pulse voltammetry (DPV) was 22.0 nmol L-1. DPV was used for simultaneous determination of 6-TG, uric acid (UA) and folic acid (FA) at the modified electrode, and for quantification of 6-TG, UA and FA in some real samples by the standard addition method.