Two simple, rapid, sensitive and accurate methods (A and B) for the microdetermination of melatonin in pure form and in pharmaceutical formulations are developed. Method A is based on the formation of tris(o-phenanthroline)iron(II) complex (ferroin) upon reaction of melatonin with an iron(III)-o-phenanthroline mixture in sodium acetate-acetic acid buffer media. The ferroin complex is colorimetrically measured at λmax 510 nm against reagent blank. Method B is based on the reduction of Fe (III) by the drug which forms a colored complex (λmax 522 nm) with 2,2-bipyridyl. Optimizations of the experimental conditions are described. Beer's law is obeyed in the concentration range 0.4 – 6.4 μg ml for A and 0.4 – 7.4 μg ml for B, respectively. The developed methods are applied successfully for the determination of melatonin in pure form and in melatonin tablets without any interference from common excipients.
|
