ELECTROCHEMISTRY OF REDOX ACTIVE DRUCS AND ITS APPLICATION TO HPLC DETERMINATION IN PHARMACEUTICAL ANALYSIS

Abstract

1,4-Dihydropyridine compounds are used mainly for the treatment of hypertension and angina through inhibition of the entry of the calcium ion to the cells. The electrochemical study of these compounds is important to investigate their mechanism of action,• stability and metabolism. This study was performed on five compounds of this group namely; barnidipine HCl, benidipine HCl, nicradipine HCl, nifedipine and isradipine. Firstly the study involved the elucidation of the mechanism of the electrochemical reaction of these compounds on glassy carbon electrode using different techniques; cyclic voltarnmetry, controlled potential electrolysis and spectroelectrochemistry. This study showed that these compounds have two electrochemicaly active centers, 1,4-dihydropyridine and nitrophenyl group in compounds I-IV or 2,1,3-benzooxodiazole in isradipine. The mechanism of the electrochemistry of these compounds on surface of glassy carbon electrode was suggested. The adsorption of these compounds on surface of gold and glassy carbon electrodes was studied by specular reflection technique. This study showed that adsorption of these compounds on surface of glassy carbon is less than that on surface of gold electrode and this indicates the validity of glassy carbon electrode for electrochemical detection in HPLC. Adsorption of these compounds on surface of gold electrode decreases by increase in pH. At alkaline pH there is no adsorption. Isradipine and nifedipine do not adsorb on surface of gold electrode at any pH and this indicates that adsorption of other studied compounds is due to the HCl salt. On surface of glassy carbon there is no adsorption at acidic or alkaline pH, while at neutral pH all compounds showed little adsorption. Quantitative study of these compounds was performed by HPLC technique using electrochemical detector in alkaline mobil phase (pH 11.8) on alumina column. The chromatographic conditions were optimized for each compound.