The Preparation And Pharmaceutically Analytical Application Of Novel Chemically Modified Sensors

1. Voltammetric determination of meloxicam in pharmaceutical formulation and human serum at glassy carbon electrode modified by cysteic acid formed by electrochemical oxidation of L-cysteineThe improvement of electrochemical detection of meloxicam is presented by modification of a glassy carbon electrode with anionic layer of cysteic acid providing electrostatic accumulation of the analyte onto the electrode surface. The modification formed by electrochemical oxidation of L-cysteine was performed by cycling potential in cystein solution. The anodic peak current obtained at + 1.088 V (vs. Ag/AgCl) by voltammetry was linearly dependent on the meloxicam concentration in the range of 4.3×10-8 ~ 8.5×10-6 M in the B-R buffer solution (0.04 M, pH 1.86) with a correlation coefficient of 0.999. The detection limit (S/N = 3) is 1.5×10-9 M. The low-cost modified electrode shows good sensitivity, selectivity and stability and has been applied to the determination of meloxicam in pharmaceutical formulation and spiked serum with satisfactory results. The electrochemical reaction mechanism of meloxicam was discussed. 2. Voltammetric determination of dopamine in human serum with amphiphilic chitosan modified glassy carbon electrodeAn improvement of selectivity for electrochemical detection of dopamine (DA) with differential pulse voltammetry is achieved by covalently modifying a glassy carbon electrode (GCE) with O-carboxymethylchitosan (OCMCS). The amphiphilic chitosan provides electrostatic accumulation of DA onto the electrode surface. In a phosphate buffer solution (pH 6.0), a pair of well-defined reversible redox waves of DA was observed at the OCMCS/GCE with aΔEp of 52 mV. The anodic peak current obtained from the differential pulse voltammetry of dopamine was linearly dependent on its concentration in the range of 6.0×10-8 to 7.0×10-6 M, with a correlation coefficient of 0.998. The detection limit (S/N = 3) was found to be 1.5×10-9 M. The modified electrode had been applied to the determination of DA in human serum samples with satisfactory results.3. Voltammetric determination of terbinafine in pharmaceutical formulations and biological fluid at glassy carbon electrode modified by multi-wall carbon nanotubes functionalized with carboxylic acid groupsTerbinafine was determined by differential pulse voltammetry (DPV) using a glassy carbon electrode modified by functionalized multi-wall carbon nanotubes (MWCNTs) in Britton-Robinson (B-R) buffer solution (0.04 M, pH 5.0). The anodic peak used was at + 0.924 V (vs. SCE). A good linear relationship was realized between the anodic peak currents and terbinafine concentrations in the range of 1.5×10-7 ~ 4.5×10-5 M with a correlation coefficient of 0.998. The detection limit (S/N = 3) was 5.0×10-8 M. The MWCNTs with negatively-charged functional groups have the advantage of high electroactive surface area, excellent electronic conductivity, and strong electrostatic affinity for terbinafine. The low-cost modified electrode showed good sensitivity, selectivity and stability, and had been applied to the direct determination of terbinafine in pharmaceutical formulations and human serum samples with satisfactory results. The electrochemical reaction mechanism of terbinafine at the modified electrode was also firstly discussed, which was two electrons and one proton irreversible oxidation process. It is hoped that the modified electrode will be applied for the clinical medically test and the pharmacokinetics in future.