CAPILLARY ZONE ELECTROPHORESIS DETERMINATION OF PHENYLALANINE IN SERUM - A RAPID, INEXPENSIVE AND SIMPLE METHOD FOR THE DIAGNOSIS OF PHENYLKETONURIA

A simple, rapid, and quantitative capillary zone electrophoresis metho d for phenylalanine analysis in serum has been developed, with the aim of providing an analytical tool, as an alternative to liquid and gas chromatography, for the routine laboratory diagnosis of phenylketonuri a. Electrophoresis was carried out in a 65 cm long, 50 mu m wide bare silica capillary, using 0.025 M berate (adjusted to pH 10 with 1 M NaO H) at a potential of 20 kV, with in-column UV detection at 214 nm. Und er these conditions, the three aromatic amino acids (tryptophan, pheny lalanine and tyrosine) migrated according to the pKs of the respective amine (and hydroxyl) groups. The efficiency of separation was about 1 50000 plates/column for phenylalanine. Diprophylline was adopted as in ternal standard. The injection of ethanol-deproteinized normal control serum gave rise to only a few major peaks not interfering with phenyl alanine; phenylalanine in serum at normal concentrations appeared in a clean region of the electropherogram as a symmetrical peak with a mig ration time of about 11 min. The sensitivity was greater than or equal to 3 mu g/mL, With s/n ratio = 3. The linearity, in the range of 5-17 5 mu g/mL, was described by the equation y = 1.407-0.583 x, r(2) = 0.9 998. Accuracy and precision were satisfactory, with intra-day and inte r-day coefficients of variation lower than 4% and 7%, respectively. Th e injection of sera from five phenylketonuria patients gave electrophe rograms clearly showing huge peaks of phenylalanine, thus allowing an easy laboratory diagnosis of phenylketonuria.