Fig. 1

GC–MS chromatograms of the MCF derivatives of GABA and D6-GABA and their mass spectra. The MCF derivative of GABA (a), D6-GABA (b), a mixture of GABA and D6-GABA (c), D6-GABA-spiked leaf sample (d), and the mass spectra of the MCF derivative of GABA (e), and D6-GABA (f). The reaction scheme of GABA and D6-GABA with MCF is also shown in the upper right corner of graph e, f