Quantitation of chiral amino acids from microalgae by micellar electrokinetic chromatography and laser induced fluorescence detection

Running Title: Chiral analysis of microalgae amino acids by MEKC-LIF ABSTRACT In this work, a chiral and a non-chiral micellar electrokinetic chromatography with laser-induced fluorescence detection (MEKC-LIF) have been combined to identify and quantify a group of D-and L-amino acids (D/L-aa) in different microalgae samples. The combination of the non-chiral and chiral-MEKC-LIF methods made easier the identification of the microalgae amino acids, previously derivatized with fluorescein isothiocianate, providing a double proof on the correct detection of these analytes. Three microalgae species, Spirulina platensis, Dunaliella salina and Tetraselmis suecica, were compared in terms of their content in D-platensis samples dried under different conditions (i.e., hot-air or lyophilized) was carried out in order to investigate the effect of the thermal processing on the D/L-aa content. Moreover, two procedures for extraction of amino acids from microalgae (i.e., a classical procedure and pressurized liquid extraction) together with diffferent conditions for amino acids derivatization were studied in order to increase the sensitivity of the whole analytical method. By using the selected chiral-MEKC-LIF conditions (100 mM sodium tetraborate, 30 mM SDS and 20 mM β-CD at pH 9.7) the main microalgae D/L-aa are separated in less than 25 min with efficiencies up to 840,000 plates/m and good sensitivity (i.e., 330 ng of D-Arg per gram of microalga could be detected by this procedure for a signal to noise ratio of three). Several D-aa were detected in all the microalgae, observing interesting differences in their D/L-aa profiles, what corroborates the usefulness of the chiral-MEKC-LIF approach to characterize different microalgae species as well as different microalgae drying processes. Moreover, it seems from the chiral-MEKC-LIF results that pressurized liquid extraction can selectively extract different free amino acids from microalgae.