Desenvolvimento de eletrodos de carbono vítreo modificados com nanotubos de carbono para a determinação de analitos de interesse farmacêutico

Abstract

In this work, the development of electroanalytical methods for the determination of methotrexate (MTX), propylthiouracil (PTU), propanolol (PROP) and verapamil (VPM) in pharmaceutical formulations is described. In these methods it was employed a glassy carbon electrode (GC) modified with dihexadecyl hydrogenphosphate (DHP) or polyallylamine hydrochloride (PAH) film containing immobilized multi-walled carbon nanotubes (MWCNTs). Initially, the electrochemical behavior of each modified electrode was studied by cyclic voltammetry at different scan rates for a 1.0 × 103 mol L1 potassium hexacyanoferrate (III) in 0.1 mol L1 potassium chloride solution. Applying the Randles-Sevcik equation, it was observed an increase of the active area of MWCNTs-DHP/GC and MWCNTs-PAH/GC electrodes of 1.5 and 3.1 times respectively in comparision with the GC electrode. The square wave voltammetry, differential pulse voltammetry and linear sweep voltammetry parameters were studied and optimized for each analyte and then it was selected the best technique for the development of the analytical method. In the developed method for MTX determination in pharmaceutical formulations, it was used the GC electrode modified with MWCNTs and DHP (MWCNTs-DHP/GC), employing differential pulse adsorptive anodic stripping voltammetry (DPAdASV) technique after the optimization of experimental conditions. The analytical curve obtained was linear in the MTX concentration range from 5.0 × 10-8 to 5.0 × 10-6 mol L-1, with a limit of detection (LOD) of 1.2 × 10-8. The MTX was quantified in commercial samples and the results compared with an HPLC method, and the relative errors ranged from -4.0 to 4.0%. An analytical method for determination of PTU in pharmaceutical formulations was also developed using a modified GC electrode with MWCNTs within a PAH film (MWCNTs-PAH/GC) and linear sweep adsorptive cathodic stripping voltammetry (LSAdCSV). After the optimization of experimental conditions, the analytical curve was linear in the PTU concentration range from 5.0 × 10-6 to 5.8 × 10-5 mol L-1, with a LOD equal to 1.0 × 10-6 mol L-1. The PTU was quantified in commercial samples and the results were compared with those results obtained using the British Pharmacopoeia method. The relative errors obtained were between -1.0 and 2.0%. Using DPAdASV technique and a MWCNTs-PAH/GC electrode, PROP was determined in pharmaceutical formulations. The analytical curve was linear in the concentrations range from 7.5 × 10-8 to 1.0 × 10-6 mol L-1 PROP, with LOD equal to 6.3 × 10-8 mol L-1 and the results were in close agreement whit those obtained using the Brazilian Pharmacopoeia method at a confidence level of 95 %. The relative standard deviation ranged from 2.5 and 1.2%. Finally, as a fourth electroanalytical method, a square wave adsorptive anodic stripping voltammetry (SWAdASV) was proposed for determination of VPM in pharmaceutical formulations using a MWCNTs-PAH/GC electrode. The analytical curve was linear over the VPM concentration range 5.0 × 10-9 - 1.0 × 10-7 mol L-1, with an LOD of 3.6 × 10-9 mol L-1 . The VPM was quantified in pharmaceutical samples and the results compared with results obtained using the method of the Brazilian Pharmacopoeia.