Selective determination of γ-aminobutyric acid, glutamate and alanine by mixed micellar electrokinetic chromatography and fluorescence detection

A mixed micellar electrokinetic chromatography method with fluorescence detection was developed to simultaneously monitor γ-aminobutyric acid (GABA), glutamate (Glu) and alanine (Ala) in biological samples. Amino acids were derivatized with naphthalene-2,3-dicarboxaldehyde (NDA). The separation of three NDA-labeled isomers (GABA, α-ABA, β-ABA) was studied in detail with different micelles solutions such as sodium dodecyl sulfate (SDS), β-cyclodextrin (β-CD) and sodium cholate (SC). Simultaneous resolution of GABA, Glu and Ala from 21 amino acids was achieved within 5 min using 20 mM phosphate buffer at pH 8.7 containing 24 mM SC and 26 mM SDS. The detection limits were 4.0 × 10−8, 1.1 × 10−8 and 1.3 × 10−8 M, for GABA, Glu and Ala, respectively, with S/N = 2. The method was applied to monitor the changes of amount of GABA, Glu and Ala in tobacco leaf in response to cold and dark stress.