The sample treatment used was: ten capsules or five tabletswere first homogenized (by grinding for tablets) and then, therequired quantity was weighed to obtain a final concentration of60 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 andthe mixture was shaken (5 min), sonicated (5 min), and centrifuged(18,353 × g) for 5 min at 25◦C. All the supernatants were col-lected in an appropriate volumetric flask that was completed withwater.