The separation was performed
on Aqua column (250 mm 4.6 mm, Phenomenex1, Aschaffenburg,
Germany) and the detection wavelength was set at 210 nm.
Eluent A was water (HPLC grade) and eluent B was acetonitrile.
Injection volume was 20 mL. Theanine standard solutions in the
range of 5–200 mg/L were prepared and used to construct
the calibration curve.