Derivatization of amino acids was performed using an AccQ-Fluor reagent kit and separation was achieved with a Waters AccQ-Tag Nova-Pak C18 column (150 3.9 mm; Waters, Dublin, Ireland) via gradient elution consisting of 9.1% (v/v) AccQ-Tag Eluent A concentrate (mobile phase A) and 60% (v/v) aqueous acetonitrile (mobile phase B).