The analytical method is in total 19 minutes long and the column used was a reverse phase BEH C18 column (50 x 2.1 mm, 1.7 μm). For separation of target AAs, mobile phase A consisted of 95:5 H2O:MeOH with 0.1 % formic acid with mobile phase B as 100 % MeOH. Flowrate was set at 0.2 mL min -1 and injection volume was 20 μL. Mobile phase starting conditions were 0 % B (held for 1 minute), then a gradual gradient to 40 % B (8.5 minutes), gradient up to 100 % B (3.5 minutes), hold of 100 % B (3 minutes) and finally dropping back to 0 % B (0.5 minutes).