Amino Acid Analysis in general can be used for identification testing of biopharmaceutical active ingredients and the determination of impurities and related substances in active pharmaceutical ingredients. It can also be used for single or total amino acid quantitation in drug products. Our objective was to develop a liquid chromatography method for simultaneous determination of approximately 20 amino acids in simple and complex mixtures that comply with the system suitability requirements of the Ph. Eur. 2.2.56.