Spectrofluorimetric determination of phenylalanine based on fluorescence enhancement of europium ion immobilized with sol–gel method

The analysis of phenylalanine (Phe) in serum is widely performed for the screening of newborn phenylketonuria (PKU). In this work, a novel spectrofluorimetric method for the determination of Phe was developed based on the fluorescence enhancement of Ruhemann's purple, the reaction product between Phe and ninhydrin, upon coordination with Eu3+. A filter paper disc containing immobilized reactants (ninhydrin and Eu3+) was fabricated by sol–gel method. The experimental parameters affecting the determination of Phe, such as the concentrations of immobilized reagents, the pH value, the reaction time and temperature were optimized. Under optimum conditions, the fluorescence intensity of Phe–ninhydrin–Eu3+ system was linearly proportional to the concentration of Phe in the range from 5 × 10−5 to 2 × 10−3 mol L−1, and the limit of detection was found to be 5.2 × 10−6 mol L−1. The relative standard deviation was 2.6% for ten replicate measurements of 1.5 × 10−4 mol L−1 of Phe. The method has merits of sensitivity, simplicity and low cost, and has been applied to the determination of Phe in artificial serum.

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► A simple, low-cost and environmentally friendly determination for phenylalanine is developed.
► Filter paper-based optical sensor is fabricated by immobilizing reactants with sol–gel technology.
► The fluorescence of RP (the reaction product between phenylalanine and ninhydrin) is remarkably enhanced upon binding to Eu3+.
► The method has great potential to be used as an alternative for the diagnosis of newborn phenylketonuria.