A spectral voltammetric and chromatographic investigation of the complexation of oxytetracycline hydrochloride to metals of varying valency

The research work presented here is concerned with how a systematic study of the acid - base equilibria, polarographic and chromatographic behaviour of an antibiotic and its corresponding metal complexes can aid in the development of a sensitive analytical method to speciate these compounds. The antibiotic studied here was one of the most used of all broad spectrum antibiotics namely oxytetracyclme hydrochloride. A systematic study of the acid - base equilibria yielded four pK^ values pK^ = 3 3, pK^ = 7.5, pK^ = 9.7 and pK^ = 10.4. A systematic study in different buffers also using ultraviolet spectroscopy yielded information which was important in determining at which sites the metals studied were binding to the antibiotic. The Cu(II), Ni(II), Co(II) and Mg(II) ions binding in a similar fashion to the BCD chromophore of the antibiotic and the Fe(II) and Fe(III) ions binding in a different manner to the A chromophore of the antibiotic. The polarographic study yielded information which was important in the identification of the process of reduction of oxytetracyclme hydrochloride. The first peak of reduction being due to the carbonyl group and its conjugated double bond in the A chromophore. The remaining reduction peaks being due to the carbonyl groups and their conjugated double bonds in the BCD chromophore. The polarographic information was also important in determining at which sites the metals studied were binding to the antibiotic , the results obtained for this were in good agreement with the spectroscopic study. A systematic study of the chromatographic behaviour of oxytetracycline hydrochloride and its corresponding metal complexes yielded information which was important in the development of an analytical method for the speciation of these antibiotic-metal complexes. The retention times obtained also reflected different binding sites in the case of the Fe(II) ion. The lability of these complexes is also discussed