Differential pulse polarography of tetracycline: determination of complexing tendencies of tetracycline analogs in the presence of cations.

The complexation tendencies, stoichiometries, and stability constants for tetracycline, minocycline, and demeclocycline with the metallic ions calcium(II), magnesium (II), zinc(II), aluminum(III), iron(II), and iron (III) were evaluated using a polarographic technique. Changes in pulse peak heights for each tetracycline deravative were measured as a function of cation concentration. The method provides an in vitro method of evaluating the selectivity of particular metal ions for different tetracycline analogs.