The present work is devoted to the analysis of the phenomenon of “double peaks” of aminoacids in High Performance Liquid Chromatography. Therefore, we have carried out some experiments in order to confirm that the appearance of several peaks from the injection of a single compound was related to different ionic forms of this compound. It could be shown that elution of multiple peaks for L-α-methyldopa did not refer to its degradation products, but to the different ionic species present in the media. The same occurred with its derivative 3-O-methylmethyldopa and with dl-phenylalanine.