Dual-Channel Continuous-Flow System for Determination of Phenylalanine and Galactose: Application to Newborn Screening

tem for the simultaneous measurement of phenytalanine and galactose from blood specimens on filter-paper. Using a single #{188}-in.-diameter(6-mm) specimen, we measure both components fluorometricallyat a rateof 70/h.Analytical recoverywiththemethod and thelinearityofmeasurements vs sample concentration are excellent through the ranges of interest, 0-200 mg/L for phenylalanine and 0-800 mg/L for galactose. Carryover at the critical values during screening, 40 mg/L for phenylalanine and 100 mg/L for galactose, is essentially zero. The dual-channel system provides the means to incorporate a low-incidence test, i.e., galactosemia (incidence 1/70 000), into an existing program for phenylala-nine analysis, for which the higher rates (phenylketonuria, incidence 1/11 500) easily justify the cost of mass screening. Additional Keyphrases: galactosemia phenylkefonuri