EVALUATION OF LC METHODS FOR THE SEPARATION OF AMOXICILLIN AND ITS RELATED SUBSTANCES

Five isocratic liquid chromatography (LC) methods have been examined f or the separation of amoxicillin and its related substances on C-18 or C-8 columns. The United States Pharmacopeia (USP) assay method gave b etter selectivity. Similar selectivity was obtained not only on C-18 c olumns but also on C-8 and poly(styrene-divinylbenzene) columns. The g ood selectivity was confirmed by a second laboratory. A resolution tes t using cefadroxil was developed for the method performance. Based on the USP method, a gradient LC method was developed for the analysis of related substances in amoxicillin. This method has been proposed for the assay and purity control in the amoxicillin monographs of the Euro pean Pharmacopoeia and will be further examined in a collaborative stu dy.