Interlaboratory study of the analysis of amoxicillin by liquid chromatography

Abstract A liquid chromatography method for analysis of amoxicillin was examined in a collaborative study involving 11 laboratories. The method comprised an isocratic part, which is used in the assay. The isocratic part is similar to the assay method for amoxicillin of the United States Pharmacopeia 23. When the isocratic part is combined with gradient elution, the method is suitable for purity control. Five samples of amoxicillin (trihydrate and sodium salt) with varying purity were analysed. The main component and the impurities were determined. An analysis of variance proved absence of consistent laboratory bias. The laboratory-sample interaction was not significant. Estimates for the repeatability and reproducibility of the method, expressed as standard deviations (SD) of the result of the determination of amoxicillin, were calculated to be 1.1 and 1.3 respectively.