Quantitative estimation of tryptophan in plasma and urine using thin-layer chromatography (TLC) and induced fluorescence

A new method for the determination of free tryptophan in plasma and urine is described. After isolation of tryptophan by thin-layer chromatography, a photometric measurement of induced ultraviolet fluorescence is used for its quantitative estimation. The intensity of induced fluorescence in ultraviolet light is directly proportional to the amount of tryptophan present. This method has advantages for it does not require previous precipitation of plasma proteins, and is not dependent on microbiological assay. Tryptophan values obtained by this method are of the same order as those found by most previous investigators, but the technique is simpler and quicker. Values for healthy young white adult males are: Fasting plasma levels: Mean of 9 subjects: 2.06 mg/100 ml; Standard Deviation (S.D.) ± 0.53; Range 1.23–2.80. 24-h urinary excretion on unrestricted diet: Mean of 7 subjects: 19.56 mg; S.D. ± 8.61; Range 9.26–35.10 mg.