An enzymatic assay for the quantitative measurement of L-phenylalanine in newborn blood spots (for neonatal screening of Phenylketonuria). This product is for Research Use Only; International customers contact your representative to receive information about the CE marked version. The Phenylalanine of the blood spots is eluated quantitavely using Trichloracetic acid (3 %) from the cellulose paper. After that the Phenylalanine is transformed by the enzyme Phenylalaninedehydrogenase to Phenylpyruvate. This reaction is coupled to the reduction of the coenzyme NAD+, present in the reaction mixture. The reduced NADH transforms in a redox reaction the added Tetrazolium salt to the yellow substrate Formazane. The amount of Formazane developed is proportional to the concentration of Phenylalanine in the sample. The color of the substrate can be measured with a photometer at 450 nm.