Electrochemical sensing of mesalazine and its N-acetylated metabolite in biological samples using functionalized carbon nanotubes.

A rapid analytical method without the time-consuming separation step was developed to simultaneously determine mesalazine and its N-acetylated metabolite. A simply designed electrochemical sensor with functionalized carbon nanotubes in a Nafion matrix was constructed for this purpose. The presence of the nanocomposite modifier on the electrode surface significantly affects the voltammetric response of target analytes. The morphology of the modified surface was investigated by scanning electron microscopy. The effect of modifier amount on the sensor performance was investigated in order to obtain the most favorable response of mesalazine since it was found in lower concentration limits in real samples then its metabolite due to the rapid drug elimination and the slightly slower renal metabolite excretion. Under optimal conditions, the anodic peak currents measured by square-wave voltammetry increased linearly after short accumulation of 30s in the range of 5.0×10(-8)-2.5×10(-6)M and 1.0×10(-7)-5.0×10(-6)M for drug and metabolite, respectively. In addition to stable response, the sensor has excellent performance associated with high sensitivity (2.33×10(7) and 8.37×10(6)µAM(-1) for drug and metabolite, respectively). The synergistic effect of the carbon nanotubes and Nafion polymer film yielded detection limit of 1.2×10(-8)M for mesalazine and 2.6×10(-8)M for its metabolite that is comparable to known chromatographic methods. Due to the easy preparation and regeneration, the proposed sensor opens new opportunity for fast, simple and sensitive analysis of drug and its metabolite in human serum samples as well as direct quantification of mesalazine in delayed-release formulations.

Multi-walled carbon nanotubes/Nafion composite film modified electrode as a sensor for simultaneous determination of ondansetron and morphine.

The electrochemical behavior of ondansetron was studied on the multi-walled carbon nanotubes/Nafion polymer composite modified glassy carbon electrode (MWCNTs-Nafion/GCE). The oxidation peak potential was shifted from 1.32 V to 1.18 V compared to the bare electrode indicating excellent electrocatalytic activity of immobilized film toward drug molecule. The modified electrode exhibited a remarkable enhancement effect on voltammetric response due to the synergistic effect of nanomaterial and cation-exchange polymer on the electron transfer rate, the effective electrode area and the accumulation capability. After optimizing the experimental parameters, adsorptive stripping procedure was used for the determination of ondansetron in pharmaceutical formulation. The results were satisfactory in comparison with those obtained by high-performance liquid chromatography. In addition, the MWCNTs-Nafion/GCE exhibited high selectivity in the voltammetric measurements of ondansetron and co-administrated drug morphine with potential difference of 430 mV. The response peak currents had linear relationship with drug concentration in the range of 1.0 × 10(-7)-5.0 × 10(-6)M and 1.0 × 10(-7)-4.0 × 10(-6)M with detection limits 3.1 × 10(-8) and 3.2 × 10(-8)M for ondansetron and morphine, respectively. The electrode was successfully applied for simultaneous electrochemical sensing of both drugs in human serum samples after selective accumulation at the electrode surface.