The sample treatment used was: ten capsules or five tablets were first homogenized (by grinding for tablets) and then, therequired quantity was weighed to obtain a final concentration of 60 g/mL of l-amino acid (an intermediate concentration withinthe calibration curve) after four consecutive water extractions. For Capsules #3 the final concentration was 120 g/mL for l-Pheand 45 g/mL for l-Tyr due to their content in the sample. Foreach extraction, 20 mL of water were added to the sample and the mixture was shaken (5 min), sonicated (5 min), and centrifuged(18,353 × g) for 5 min at 25◦C. All the supernatants were collected in an appropriate volumetric flask that was completed with water.