Simultaneous determination of phenylalanine and tyrosine in peripheral capillary blood by HPLC with ultraviolet detection

Phenylalanine (Phe) and tyrosine (Tyr) are the most reliable indicators for the diagnosis of phenylketonuria (PKU). The purpose of this study is to establish a simple and rapid method for the determination of Phe and Tyr in peripheral capillary blood from newborns and children by high performance liquid chromatography with ultraviolet detection (HPLC-UV). Peripheral blood specimens were taken from newborns or children by heel stick or skin puncture on the fingers. Blood samples were deproteinized by equal volume of 5% perchloric acid. Amino acid separation was carried out on a Hypersil C8 column. The mobile phase containing 5% acetonitrile (v/v) was run at a flow rate of 1.5 mL/min. Phe and Tyr were determined in the ultraviolet detector at 210 nm. The determination was within 10.0 min. The linear range was from 6.0 to 1512.0 μmol/L for Phe and 5.5 to 1250.0 μmol/L for Tyr. Although Phe and Tyr levels from peripheral blood samples were relatively lower than those from serum or plasma, the data showed a good agreement between them. The method we developed is simple, rapid and convenient. It is useful for screening and diagnosis of PKU in newborns and children.