Simultaneous determination of amino acids in tea leaves by micellar electrokinetic chromatography with laser-induced fluorescence detection

A rapid and effective method of micellar electrokinetic chromatography with laser-induced fluorescence detection was developed for the simultaneous determination of amino acids in tea leaves. Pre-column derivatization of the analytes used 4-chloro-7-nitrobenzofurazan (NDB-Cl). Optimal separation was achieved at +20 kV using an uncoated fused silica capillary (40.0 cm effective length, 50.2 cm total length, 75 μm internal diameter), as well as 20 mM sodium borate (pH 8.5), 20 mM Brij 35, and acetonitrile 10% (v/v) as running buffers. Within 11 min, 15 amino acids were separated completely. The optimized method demonstrated good linearity (r2 ⩾ 0.9990), precision (⩽6.65%), accuracy (85.50-112.74%), and sensitivity (0.1 ng/mL-100 ng/mL). The method successfully determined the quantity of amino acids in five different tea leaves; furthermore, theanine was identified as the most abundant amino acid in teas. The proposed method showed great potential in further investigations on the biofunctions of different tea samples.