Electron Paramagnetic Resonance Method for the Quantitative Assay of Ketoconazole in Pharmaceutical Preparations

Abstract

In this study, electron paramagnetic resonance (EPR) is used, for the first time, as an analytical tool for the quantitative assay of ketoconazole (KTZ) in drug formulations. The drug was successfully characterized by the prominent signals by two radical species produced as a result of its oxidation with 400 microg/mL cerium(IV) in 0.10 mol dm(-3) sulfuric acid. The EPR signal of the reaction mixture was measured in eight capillary tubes housed in a 4 mm EPR sample tube. The radical stability was investigated by obtaining multi-EPR scans of each KTZ sample solution at time intervals of 2.5 min of the reaction mixing time. The plot of the disappearance of the radical species show that the disappearance is apparently of zero order. The zero-time intercept of the EPR signal amplitude, which should be proportional to the initial radical concentration, is linear in the sample concentration in the range between 100 and 400 microg/mL, with a correlation coefficient, r, of 0.999. The detection limit was determined to be 11.7 +/- 2.5 microg/mL. The method newly adopted was fully validated following the United States Pharmacopeia (USP) monograph protocol in both the generic and the proprietary forms. The method is very accurate, such that we were able to measure the concentration at confidence levels of 99.9%. The method was also found to be suitable for the assay of KTZ in its tablet and cream pharmaceutical preparations, as no interferences were encountered from excipients of the proprietary drugs. High specificity, simplicity, and rapidity are the merits of the present method compared to the previously reported methods.

Electron paramagnetic resonance monitoring for on-demand electrochemically-generated radicals

“…This lead supports the analysis of the KTZ-oxidation products in more details. It is also indicates that, unlike our earlier investigation of the chemical oxidation of KTZ-radical species [18] that suggested KTZ oxidation produced imidazole and acetamide radical species in different proportions, the current work proves that the KTZ fragmentation occurs at the acetamide-piperazine side to produce two nitroxide radical species.…”

“…The present cell provided a maximal sensitivity and a minimal dielectric loss along the central axis of the EPR cavity, easy handling, and mounting with no additional adjustments, as it used a small analyte volume in a disposable capillary tube. The EC-EPR studies involving KTZ indicated that the concentration range required for acetamide radical generation was ten times (10-50 ppm) less than the concentration required for the chemical oxidation method (100-400 ppm) in the presence of Cerium(IV) in sulfuric acid media [18], as it was based on radical creating rather than radical disappearance during a chemical process analysis. The use of a graphite pencil electrode (GPE) as a working electrode surface reduced uncertainty into concentration estimates via the chemical oxidation, which required a high concentration of KTZ in multiple capillary tubes.…”

“…Unlike our recently reported chemical oxidation of the acidified KTZ by Ce(IV) [18], the current EC-oxidation relies on the radicals' formation rather than disappearance, which enables the 'on-demand' formation of radicals at disposable graphite pencil electrode (GPE) surfaces by alternating the applied potential between 'ON' and 'OFF' states. It is also used to elucidate the kinetic of the acidified KTZ oxidation and to identify its oxidative products that could be linked to its delivery in acidic solutions.…”

“…Spectroscopic techniques, such as X-ray [1][2][3][4][5], infrared (IR) and Raman [6][7][8][9], UV-vis [10][11][12], nuclear magnetic resonance (NMR) [13][14][15], and EPR [16][17][18][19] spectroscopies are versatile tools for chemical analysis, particularly in the pharmaceutical and biopharmaceutical fields. Many of these spectroscopic techniques are routinely utilized in drug applications, such as characterizing formulations or elucidating the kinetic processes associated with drug delivery.…”

Electron and proton magnetic resonance spectroscopic investigation of anthracene oxidation

“…Due to the growing interest in radical detection and identification, electron paramagnetic resonance (EPR) spectroscopy is uniquely suited as a technique for monitoring free radical kinetics. We have previously reported using EPR spectroscopy as an analytical tool for free radical intermediates generated by different oxidation processes such as the irradiation of alanine [ 19 ] and the chemical and electrochemical oxidations of active ingredients in drug formulations [ 20 , 21 ]. In this work, we report the investigation of the free radical reactions of anthracene in concentrated sulfuric acid using EPR spectroscopy, which can be seen as a model system for other PAHs.…”