Novel electrochemical strategy for determination of 6-mercaptopurine using anodically pretreated boron-doped diamond electrode

A novel electrochemical approach for 6-mercaptopurine (6-MP) determination employing an anodically pretreated boron-doped diamond electrode (AP-BDDE) is presented herein. The electrode reaction of 6-MP on AP-DDE (AP achieved by application of +3 V for 180 sin 1 M H2SO4) was represented by three well distinguished oxidation peaks at +0.25 V, +1.19 V and +1.63 V (P1-P3) and one reduction peak at +0.11 V (vs. Ag/AgCl/3 M KCl) in Britton-Robinson buffer with pH 2. More detailed study revealed a mixed adsorption and diffusion-controlled reaction mechanism of the analyte. Differential pulse voltammetry (DPV), adapting favorable working conditions found by cyclic voltammetry, was developed for the sensitive determination of 6-MP. A possibility to analyze three baseline separated peaks provided valuable selectivity enhancement of the method. The overall best analytical performance was achieved for the third oxidation peak (P3), which offered the highest sensitivity (30.4 nA/mu M) and the widest linear concentration range (1-450 mu M with two independent linear segments, R-2 = 0.997). Submicromolar detection limit (0.51 mu M) and intra-day and inter-day repeatability (RSD = 0.38 and 1.91%, respectively) underlined favorable performance of the developed method. The applicability of the proposed method was illustrated by the analysis of pharmaceutical dosages containing 6-MP and spiked human urine, with an excellent average recovery of 101.8% and 95.9%, respectively. Clearly, the combination of an innovative electrode material (BDD) and sensitive voltammetric technique (DPV) established a simple and highly reliable alternative to chemically modified electrodes that might be advantageous in routine pharmaceutical and clinical analysis.