In pyridineformic acid buffer and tetramethylammonium chloride solution of pH 4.5 at a dropping mercury or a glassy carbon electrode, nitrofurazone, furazolidone and nitrofurantoin are reduced in a single six-electron wave, while chloramphenicol and other structurally related nitro derivatives are reduced in only one four-electron wave, the nitro group being reduced to the amine or to the hydroxylamine, respectively. The electrochemical behaviour of these compounds depends mainly on the nature and position of the substituents. Reduction to the primary amine occurs when the substituents possess available JC electrons to conjugate with the nitro group of the aromatic ring, which determines the transformation of the hydroxylamine into the aminevia formation of a highly reducible intermediate imine or a quinonoid structure. In contrast, if the formation of the intermediate imine is made impossible by an adverse effect of the substituent, the hydroxylamine does not undergo further reduction.Cyclic voltammograms were recorded at different pH values and at different scan rates in order to identify certain relatively unstable species. The effect of pH on the diffusion-limited current and on the €&values of the polarographic waves was also studied and the results obtained were compared with those obtained by cyclic vol ta m met ry.On this basis, and according to the polarographic and cyclic voltammetric data, a reduction mechanism for the nitrofuran derivatives is suggested, in which the importance of the homogeneous chemical reactions associated with the electron-transfer steps is examined.

The polarographic behaviour of nitrofurantoin and chloramphenicol have been studied in pyridineformic acid buffer and tetramethylammonium chloride solution at pH 4.3. The €4 versus pH and ilim versus pH relationships show that the values are pH dependent and that the current is independent of pH except when acidbase equilibria affect it. The difference in €+ values (230 mV) makes simultaneous determination possible. Simultaneous determinations of both drugs were performed in a concentration range suitable for application to pharmaceutical formulations and body fluids. Other nitro derivatives can also be determined without interference. The standard additions technique provided results as satisfactory as the use of a calibration graph. The proposed method has the advantage over previously used electrochemical methods of not requiring prior separations.

In pyridineformic acid buffer and tetramethylammonium chloride solution over the pH range 0-8.5, nitrofurazone, furazolidone and other nitrofuran derivatives are reduced in a six-electron process, giving rise to a well defined polarographic reduction wave at a dropping mercury electrode. The current is diffusion controlled and proportional to the concentration from about 5.88 x 10-3 M to the limit of detection of 1.24 x 1 0 -6 ~. The proposed method permits these drugs to be determined, without any prior separation or extraction, in pharmaceutical formulations and in urine at levels at which the unchanged drugs are excreted.Other drugs commonly used as therapeutic agents, such as nitro derivatives of 1 ,4-benzodiazepinesr chloramphenicol, metronidazole and tinidazole, are reduced in a single four-electron process at more negative potentials, which makes simultaneous determinations possible.Keywords : Nitro fu razone de te rm ina tion; fu razolidone determination; pola rog rap h y; pha rmaceu tical formulations; urine Paper A61430

The electrochemical reduction of 7-nitro-I ,4-benzodiazepin-2-ones and of their acid hydrolysis products, 2-amino-5-nitrobenzophenonesf was studied by polarography and cyclic voltammetry in a solventbuffer system containing pyridine, formic acid and tetramethylammonium chloride solution in order to elucidate the effect of the nature and position of the substituents on the reduction of the nitro group. It was found that these two types of compounds can be polarographically and voltammetrically distinguished and that their reduction mechanisms differ owing to a structural change in substituents located at a para-position relative to the nitro group. Based on polarographic and cyclic voltammetric data, reduction mechanisms for these two species are proposed in which the donoracceptor properties of the substituents and the importance of the chemical reactions associated with the electron-transfer steps are indicated. Keywords: 7-Nitro -I , 4-benzo diazep in -2-one; 2 -am in o-5-n itro benzop h e n o n e; p o la rog rap h y; cyclic vo ltam -Paper 91006086

No abstract