Monitoring of intermediates of clioquinol electro-oxidation by thin-layer spectral and electrophoretic electrochemistry

Laser-scribed Graphene Electrodes Functionalized with Nafion/Fe3O4 Nanohybrids for the Ultrasensitive Detection of Neurotoxin Drug Clioquinol

The analysis of pharmaceutical active ingredients plays an important role in quality control and clinical trials because they have a significant physiological effect on the human body even at low concentrations. Herein, a flexible three-electrode system using laser-scribed graphene (LSG) technology, which consists of Nafion/Fe₃O₄ nanohybrids immobilized on LSG as the working electrode and LSG counter and reference electrodes on a single polyimide film, is presented. A Nafion/Fe₃O₄/LSG electrode is constructed by drop coating a solution of Nafion/Fe₃O₄, which is electrostatically self-assembled between positively charged Fe₃O₄ and negatively charged Nafion on the LSG electrode and is used for the first time to determine a neurotoxicity drug (clioquinol; CQL) in biological samples. Owing to their porous 3D structure, an enriched surface area at the active edges and polar groups (OH, COOH, and -SO₃H) in Nafion/Fe₃O₄/LSG electrodes resulted in excellent wettability to facilitate electrolyte diffusion, which gave ∼twofold enhancement in electrocatalytic activity over LSG electrodes. The experimental parameters affecting the analytical performance were investigated. The quantification of clioquinol on the Nafion/Fe₃O₄/LSG electrode surface was examined using differential pulse voltammetry and chronoamperometry techniques. The fabricated sensor displays preferable sensitivity (17.4 μA μM^-1 cm^-2), a wide linear range (1 nM to 100 μM), a very low detection limit (0.73 nM), and acceptable selectivity toward quantitative analysis of CQL. Furthermore, the reliability of the sensor was checked by CQL detection in spiked human blood serum and urine samples, and satisfactory recoveries were obtained.

Review on analytical studies of some pharmaceutical compounds containing heterocyclic rings: brinzolamide, timolol maleate, flumethasone pivalate, and clioquinol

Background

The heterocyclic compounds are extremely important with wide array of synthetic, pharmaceutical, and industrial applications. Heterocyclic-containing compounds have been reported for their broad spectrum of biological activities including antibacterial, antifungal, antiviral, antiprotozoal, and anthelmintic activity.

Main text

Several techniques have been used for the quantitation of heterocyclic compounds in pharmaceutical samples such as high-performance liquid chromatography (HPLC) either equipped with UV-visible or fluorescence, in addition to liquid chromatography-mass spectroscopy, UV-visible spectrophotometry, and electrochemical techniques. This article reviewed several published methods that have been applied to detect and quantify some pharmaceutical drugs containing heterocyclic compounds focusing on four drugs: brinzolamide, timolol maleate, flumethasone pivalate, and clioquinol.

Conclusion

From literature reviews, HPLC is the most widely used analytical technique for the quantitative analysis of the four selected drugs.