A method for the analysis of tetracycline, chlortetracycline, and oxytetracycline by alternating-current polarography was develo ed. The method agrees favorably with microbiological assays and was shown to ! e ap licable to medicinals containing these antibiotics. It was more sensitive and faster &an direct-current polarography. Qualitative and quantitative determination of oxytetracycline in the presence of chlortetracycline appears to be possible. The effect of p H and degradation of these antibiotics on polarographic response in comparison to biological activity are discussed.
EVERAL
METHODS have been described for the S determination of the tetracycline antibiotics. The microbiological methods are tedious and time consuming, and the chemical methods are, in general, not of adequate specificity. Chlortetracycline and oxytetracycline alone and in mixtures have been determined by direct-current (d.-c.) polarography (3-7, 14, 18). Recently, Daftsios and Schall (2) applied alternating-current (a.-c.) polarography t o the routine determination of 3,5-dinitrohenzamide and N-acetyl-N-(4-nitro-phenyl)sulfanilamide.
This suggested the possible use of a.-c. polarography for the routine determination of the tetracyclines.
A method was developed for the quantitative and qualitative determination of these antibiotics b y a.-c. polarography. The determination of oxytetracycline in the presence of chlortetracycline also was demonstrated. The method was shown to be as accurate as conventional methods and can be applied easily t o routine analyses of pharmaceuticals.
To the authors' knowledge, there have been no studies which utilize 8.-c. polarography for the determination of the tetracyclines.
EXPERIMENTAL
Apparatus
A Sargent model XXI polarograph modified to record a,-c. polarograms, as described by Miller (12, 13), was employed. A Beckman pH meter, model 76 (expanded scale), and an electrolysis vessel of the mercury pool type were used. Size is not critical; however, a microtype vessel with a 3-ml. total volume was employed. Reagents (85%) in absolute methanol (v/v) (1:40). Acid-Methanol Solution.-Two per cent HaPo4