Separation and determination of amino acids by micellar electrokinetic chromatography coupling with novel multiphoton excited fluorescence detection

In this article, it was demonstrated that separation and determination of 20 amino acids were accomplished by micellar electrokinetic chromatography (MEKC) coupling with novel multiphoton excited fluorescence (MPEF) detection method. Different from MPEF achieved by expensive fs laser, continuous wave (CW) diode laser of ultra-low cost was uniquely employed in our MPEF system. Amino acids were fluorescently labeled with fluorescein isothiocyanate (FITC), and were subjected to sodium dodecyl sulfate (SDS)-based MEKC separation and CW-based MPEF detection. The result was compared with that by single photon excited fluorescence (SPEF), which indicated that MPEF had the advantages of better mass detectability and higher separation selectivity over SPEF. Quantitative analysis was performed and revealed linear dynamic range of over 2 orders of magnitude, with mass detection limit down to ymole level. To evaluate the reliability, this method was successfully applied for analyzing a commercial nutrition supplement liquid.