Determination of aromatic amino acids by ion-pair reversed-phase liquid chromatography in human sera from healthy and phenylketonuric individuals.

A simple chromatographic procedure is described for simultaneous analysis of aromatic amino acids in serum samples obtained from normal individuals and from phenylketonuric patients. Quantitative measurement of phenylalanine, tyrosine, histidine and tryptophan is made in samples as small as 10 microliter after deproteinization with trichloroacetic acid. With phenoxyacetic acid as the internal standard, samples are analyzed by reversed-phase chromatography isocratically by an ion-pairing agent in the eluent, and the amino acids are detected with the UV detector at 210nm. Total analysis time was about 30 minutes. Using this method in serum samples from phenylketonuric patients phenylalanine was increased (as expected), and histidine was decreased, at a statistically significant level.