INTERLABORATORY STUDY OF THE ANALYSIS OF AMPICILLIN BY LIQUID-CHROMATOGRAPHY

A liquid chromatographic method for the analysis of ampicillin was exa mined in a collaborative study involving seven laboratories. The metho d included an isocratic part, which is used in the assay. The isocrati c part is similar to the assay method for ampicillin of the US Pharmac opeia XXIII Revision. When the isocratic part is combined with gradien t elution, the method is suitable for purity control. Six samples of a mpicillin (anhydrous, trihydrate and sodium salt) with varying purity were analysed. The main component and related substances were determin ed. An analysis of variance proved the absence of consistent laborator y bias. The laboratory-sample interaction was significant. Estimates o f the repeatability and reproducibility of the method, expressed as st andard deviations of the result of the determination of ampicillin, we re calculated to be about 0.9 and 1.1 respectively.