SEPARATION OF DIFFERENT IONIC FORMS OF L-α-METHYLDOPA AND OTHER AMINO ACIDS BY REVERSED-PHASE ION-PAIR HIGH PERFORMANCE LIQUID CHROMATOGRAPHY.

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. The separation between ionic forms was possible due to the use of sodium heptanesulphonate, an anionic ion-pairing reagent, which selectively interacts with different charged species. These findings show that equilibrium species can be separated by an appropriate analytical method, depending on the employed conditions. [ABSTRACT FROM AUTHOR]