Gas chromatographic-mass spectrometric method for quantitation of phenylalanine and tyrosine in serum

A validated gas chromatographic-mass spectrometric method for quantitation of phenylalanine and tyrosine, in serum is described. Quantitation of pheny lalanine and tyrosine with a non-labelled non-endogenous internal standard, L-2-chlorophenylalanine, compared favourably with isotope dilution mass sp ectrometric quantitation. The 95% reference ranges for phenylalanine, tyros ine and the phenylalanine-tyrosine molar ratio in neonate cord blood serum were determined by isotope dilution mass spectrometry and were found to be 77.1-144.7, 33.3-109.3 mu mol/l and 1.1-3.0, respectively. (C) 2001 Elsevie r Science B.V. All rights reserved.