The International Journal of Romanian Society of Endocrinology / Registered in 1938

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October - December 2015, Volume 11, Issue 4
General Endocrinology

Ladasiu Ciolacu FC, Ardelean A, Mândrutiu I, Belengeanu AD, Bechet D, Mihali CV, Petrescu C-M, Benga G

A Simple and Sensitive Procedure for Assessment of Plasma Phenylalanine ana Tyrosine by HPLC

Acta Endo (Buc) 2015, 11 (4): 431-435
doi: 10.4183/aeb.2015.431

Introduction. The determination of phenylalanine (Phe) and tyrosine (Tyr) levels in blood plasma is very important not only in early diagnostic, but also in monitoring the treatment of phenylketonuria (PKU). Purpose. We present a simple, sensitive and accurate procedure to determine simultaneously the plasma concentrations of Phe and Tyr. Procedure. The measurement involves two steps: a) separation of plasma (from blood prelevated on heparin), isolation and preparation of a concentrated solution of amino acids (by ion-exchange column chromatography on Dowex- 50X8), and b) determination of Phe and Tyr concentrations in the solution of amino acids by HPLC (using a Dionex Ultimate 3000 instrument equipped with a diode array detector). The analytical column was a Thermo Scientific Acclaim 120, C18, 5 μm Analitic (4.6 x 250 mm), coupled with an Acclaim C18 guard column. The values of Phe and Tyr concentrations in plasma of several patients were calculated using a calibration curve made with standards of Phe (1834.4 μmol/L in deionized water) and Tyr (600 μmol/L in deionized water). Concentrations as low as 24 μmol/dL of Phe and 15 μmol/dL of Tyr could be determined. Conclusion. The whole procedure presented here is relatively simple, rather inexpensive, however very sensitive and accurate. Consequently, it is very adequate for confirming the diagnosis of PKU in patients with neonatal hyperphenylalaninemia, as well as for monitoring the plasma concentrations of Phe and Tyr in patients with PKU.

Keywords: phenylalanine, tyrosine, phenylketonuria, hyperphenylalaninemia, plasma, HPLC, high-performance liquid chromatography.

Correspondence: Gheorghe Benga, MD, PhD, The Gheorghe Benga Foundation, Aleea Muscel No. 19, Ap. 11, 400076, Cluj-Napoca, Romania, E-mail: