“…Currently, various analytical techniques including nuclear magnetic resonance (NMR) (Schicho et al, ; Stoop et al, ), capillary electrophoresis, gas chromatography and liquid chromatography (LC), combined with various detection systems, such as fluorescence detection, ultraviolet detection, electrochemical detection and mass spectrometry (MS), have been developed for quantification of AAs in the biological fluids (Hirayama & Soga, ; Poinsot, Ong‐Meang, Gavard, & Couderc, ; Kvitvang, Andreassen, Adam, Villas‐Bôas, & Bruheim, ; Chen et al, ; Peris‐Vicente, Gimeno Adelantado, Carbó, Castro, & Reig, ; Rodier et al, ). Because most AAs show high polarity with low molecular weight, a derivatization step is often applied to achieve better retention on the reversed‐phase column (Armenta et al, ; Kaspar et al, ; Sánchez‐López, Crego, & Marina, ; Wang et al, ). For example, Thomas Themelis et al determinated glutathione using 1,4‐naphthoquinione as a derivazation reagent (Themelis, Gotti, & Gatti, ).…”