Renewable stationary phase liquid magnetochromatography: determining aspartame and its hydrolysis products in diet soft drinks.

A new chromatographic modality that does not require high pressures and also allows renewal of the stationary phase as desired is reported. The technique is based on a thin layer paramagnetic stationary phase (Fe3O4-SiO2) retained on the inner wall of a minicolumn through the action of an external magnetic field, which also plays an important role in separating the analytes. Accordingly, the name "renewable stationary phase liquid magnetochromatography", or RSP-LMC, has been proposed for it. The technique was used to separate and quantify the sugar substitute alpha-aspartame and its constituent amino acids (hydrolysis products), L-aspartic acid and L-phenylalanine, in diet fizzy soft drinks. When the results obtained for alpha-aspartame were compared with those obtained using HPLC as a reference method, no significant differences were observed. The system proposed is fully automated, making it an economic, competitive alternative to conventional methods of determining alpha-aspartame and its amino acid components.