Simultaneous measurement of phenylalanine and tyrosine by high performance liquid chromatography (HPLC) with fluorescence detection

Objectives: An HPLC method was developed to quantify serum concentrations of phenylalanine and tyrosine simultaneously using fluorescence detection without derivatization. Methods: Serum protein is precipitated with trichloroacetic acid, 0.015 mM dihydrogen-phosphate solution is used for separation on reversed-phase C-18 material, and acetonitrile is avoided. Both amino acids are monitored utilizing their natural fluorescence at 210 nm excitation and 302 nm emission wavelengths. Results: One analytical run is completed within 7 min. Lower detection limit for Phe and Tyr is 0.3 mu M. Comparison of the new method with a classical HPLC method for total amino acids and using UV-absorption detection reveals a highly significant relationship for Phe and Tyr. Conclusion: The new HPLC method allows rapid and very sensitive measurement of phenylalanine and tyrosine concentrations. (C) 2013 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.