Determination of nifedipine using nanostructured electrochemical sensor based on simple synthesis of Ag nanoparticles at the surface of glassy carbon electrode: Application to the analysis of some real samples

1. Lipid peroxidation in rat brain slices was induced by Fe+3/ascorbate. 2. Brain lipid peroxidation, as measured by malondialdehyde formation, was inhibited by all the tested nitro aryl 1,4-dihydropyridine derivatives over a wide range of concentrations. The time-course antioxidant effects of the most representative agents were assessed. On the basis of both time-course and IC50 experiments the tentative order of antioxidant activity on rat brain slices could be: nicardipine>nisoldipine> (R,S/S,R)-furnidipine > (R,R/S,S)-furnidipine>nitrendipine>nimodipine> nifedipine. 3. 1,4-Dihydropyridine derivatives that lack of a nitro group in the molecule (isradipine, amlodipine) also inhibited lipid peroxidation in rat brain slices but at higher concentrations than that of nitro-substituted derivatives. 4. All the tested nitroso aryl derivatives [2,6-dimethyl-4-(2-nitrosophenyl)-3,5-pyridinedicar. boxylic acid dimethyl ester (NTP), nitrosotoluene, nitrosobenzene] were more potent inhibitors of lipid peroxidation than were the parent nitro compounds. In conclusion, on the basis of the IC50 values determined, the rank order of antioxidant potency for these derivatives can be established as: ortho-nitrosotoluene>NTP>nitrosobenzene.

Antioxidant Effects of 1,4-Dihydropyridine and Nitroso Aryl Derivatives on the Fe+3/Ascorbate-Stimulated Lipid Peroxidation in Rat Brain Slices

The electrochemical behavior of several calcium antagonists of the dihydropyridine family has been investigated in aqueous buffered solution using a glassy carbon electrode. Both oxidation of the dihydropyridine ring and the reduction of the nitro or benzoxadiazole moiety are observed using cyclic voltammetry and the shape of the voltammograms depending on the initial scan direction. Each process may interfere with the other. The single reduction peak corresponds to a four‐electron transfer giving rise to the hydroxylamine. Reversing the scan leads to the nitroso derivative, its reversibility depends on the 2‐ or 3‐position of the nitro group. Oxidation of the dihydropyridine ring proceeds through a two‐electron exchange. However, nicardipine, which possesses a dialkylbenzylamine side chain, exhibits two additional peaks; the first due to the methoxylation of the side chain, and the second attributed to the oxidative chlorination of this moiety. Potentials are pH dependent. A general EC mechanism is proposed for the overall process. Copyright © 1992 VCH Publishers Inc.

Cyclic voltammetric study of some calcium antagonist dihydropyridines in aqueous medium

Four simple, sensitive and accurate spectrophotometric methods have been developed for the determination of nifedipine in pharmaceutical formulations. These methods are based on the formation of ion-pair complexes of amino derivative of the nifedipine with bromocresol green (BCG), bromophenol blue (BPB), bromothymol blue (BTB) and eriochrome black T (EBT) in acidic medium. The coloured products are extracted with chloroform and measured spectrophotometrically at 415 nm (BCG, BPB and BTB) and 520 nm (EBT). Beer's law was obeyed in the concentration range of 5.0-32.5, 4.0-37.5, 6.5-33.0 and 4.5-22.5 microg ml(-1) with molar absorptivity of 6.41 x 10(3), 4.85 x 10(3), 5.26 x 10(3) and 7.69 x 10(3) l mol(-1) cm(-1) and relative standard deviation of 0.82%, 0.72%, 0.66% and 0.68% for BCG, BPB, BTB and EBT methods, respectively. These methods have been successfully applied for the assay of drug in pharmaceutical formulations. No interference was observed from common pharmaceutical adjuvants. Statistical comparison of the results with the reference method shows excellent agreement and indicates no significant difference in accuracy and precision.

Extractive spectrophotometric methods for the determination of nifedipine in pharmaceutical formulations using bromocresol green, bromophenol blue, bromothymol blue and eriochrome black T.

An electrochemical method employing a β-cyclodextrin modified carbon nanotube paste electrode (βCD-CNT-PE) has been developed for the determination of nifedipine (NIF). Cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse adsorptive stripping voltammetry were utilized to study the electrochemical behaviour of NIF. The surface morphology of the electrodes has been studied by scanning electron microscopy. Studies reveal that the irreversible oxidation of NIF was highly facile on βCD-CNT-PE for which a plausible mechanism is proposed. The optimized linear working range and detection limit (S/N = 3) are 4.77 × 10−8 to 2.00 ×10−5 and 1.48 × 10−8 M, respectively. The analytical application of the modified electrode is demonstrated by determining NIF in pharmaceutical formulations and biological fluids (urine and serum). Further, the ease of preparation with high sensitivity, low detection limit and excellent reproducibility makes the proposed method highly advantageous for NIF determination.

E. Barnafi

Papers

Nifedipine: Differential pulse polarography and photodecomposition.