Phenylalanine(Phe) and Tyrosine(Tyr) were extracted from dry blood spots with 0.1% mol/L HCl-methanol. The proteins in the extraction were revomed by centifuging. Phe and Tyr were treated with 3.0 mol/L HCl-butanol. Phe and tyr butyl esters were treated with trifluoro acetic anhydride. the derivatives from Phe and Tyr were analyzed by GC-MS. The contents of the two amino acids in blood samples were determined by calculating the areas of their derivatives with reference to an exterior standard. Finally the diagnosis of PKU was made on the basis of the molar content ratios of Phe to Tyr.

Key words: CHROMATOGRAPHY-MASS SPECTROGRAPHY, AMINOACIDURIA, AMINO ACID, PHENYLALANINE, TYROSINE