Benzodiazepines, polarography

Chlordiazepoxide is the pioneer member of the 1,4-benzodiazepines to be employed clinically as an antianxiety agent in humans. A number of methods based on extraction processes are available for the assay of this drug, namely spectrofluorometry, polarography and electron-capture GC-technique but RIA measures it directly in the blood without involving extraction and possesses very low sensitivity. 

The 1,4-benzodiazepine class of pharmaceuticals (see Fig. 26.6), which are in widespread clinical use today, all possess intrinsic electrochemical activity that renders them ideal for voltammetric studies. Senkowski et al. were the first to perform a comprehensive study of this class of compounds by polarography [77] and demonstrated that the 1,4-benzodiazepines show a wave for the two-electron reduction of the 4,5-azomethine electrophore in a supporting electrolyte of 0.1 M HCI containing 20% methanol. Secondary polarographic waves... 

Flurazepam and two of its metabolites have demonstrated reversible hydrolysis of the 4,5-azomethine [131]. In acid solution, this reaction may be monitored employing pulse polarography to measure the decrease in concentration of the 4,5-azomethine of the 1,4-benzodiazepine or increase in carbonyl concentration of the open benzophenone (see Fig. 26.10). 

Polarographic methods have been extremely useful for the determination of the urinary excretion of the 1,4-benzodiazepines. An assay that employs selective solvent extraction and acid hydrolysis of diazepam and its major metabolites, iV-desmethyldiazepam and oxazepam, to their respective benzophe-nones has been employed to measure the urinary excretion of diazepam [183]. A pulse polarographic assay has been reported that will measure the urinary excretion of bromazepam following a single 12-mg dose [184]. The assay employs selective extraction of bromazepam and the 2-amino-5-bromobenzoyl-pyridine metabolite from the deconjugated metabolites, 3-hydroxybromazepam and 2-amino-3-hydroxy-5-bromobenzoylpyridine, into separate diethyl ether fractions. The residues of the respective extracts are dissolved in phosphate buffer (pH 5.4) and analyzed by pulse polarography, which yields two distinct... 

In this chapter, the application of polarography in the determination of benzodiazepines is emphasized in which this method has played an outstanding role but it can be also useful with some other psychotherapeutics such as fluorine-substituted butyrophenones [240] or those with seven-membered, possibly heterocyclic rings [241] such as in imipramine. In the latter case, anodic oxidation waves are obtained with rotated noble metal electrodes. 

The analytical applications of polarography in the benzodiazepine series are based on thorough theoretical foundations [223-228]. The mechanisms of the electrode processes are known, the electron consumptions have been determined coulometrically, and the products of the electrode reaction have been isolated in most cases. This not only allows a reliable choice of the analytical conditions but it also enables us to draw important conclusions as regards preparative electrochemistry. 

Determination of Water Soluble Imid-azo-1,4-benzodiazepine in Blood by Electron-Capture Gas-Liquid Chromatography and in Urine by Differential Pulse Polarography J. Chromatogr. 145(1) 81-96 (1978) ... 

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