Determination of flavonoids in Eruca and Diplotaxis rocket salad species: MEKC-DAD method establishment and comparison with HPLC-DAD-MS

The phenolic compounds in ten rocket salad samples were determined in this study using micellar electrokinetic chromatography (MEKC). A detailed method optimisation plan was performed to separate the phenols in rocket salad with the following four separation parameters: buffer concentration, buffer pH, applied voltage and temperature. The best results in terms of peak resolution and reproducibility among separations were obtained with a MEKC running buffer (pH 9.0) composed of 40 mM sodium tetraborate and 15 mM SDS. Using this new MEKC method, it was possible to separate the flavonoids in less than 5 min. The results obtained by MEKC analysis were compared with the data obtained by high-performance liquid chromatography (HPLC) coupled with DAD and MS detectors. The polyphenol study by HPLC-DAD-MS allowed the identification of two different classes of compounds. Quercetin and kaempferol derivatives were determined in the Diplotaxis and Eruca species, respectively. A positive correlation of phenolic compounds identified by MEKC and HPLC was found.