Gas chromatography–mass spectrometry method for determination of phenylalanine and tyrosine in neonatal blood spots

In this paper we developed a simple, rapid and sensitive method for the quantitative analysis of phenylalanine (Phe) and tyrosine (Tyr) in dried blood spots of newborns by gas chromatography–mass spectrometry (GC–MS). Phe and Tyr in blood samples were reacted with N-methyl-N-(tert.-butyldimethylsilyl)trifluoroacetamide at 120 °C for 30 min and their corresponding single derivatives were obtained. Phe and Tyr were determined by measurement of their derivatives by GC–MS in the selected ion monitoring mode. Contents of Phe and Tyr in blood spots were calculated by external standard method. The ratio of Phe to Tyr was used for neonatal screening for phenylketonuria. The present method only took a few minutes to perform and required minimal sample preparation. In addition it provided low detection limits of 1.2 μmol l−1 for Phe and 1.6 μmol l−1for Tyr.