Determination of L-tyrosine by beta-cyclodextrin sensitized fluorescence quenching method.

A novel beta-cyclodextrin (beta-CD) sensitized fluorescence quenching method for the determination of l-tyrosine (l-Tyr) with Mo(VI)-phenyl-fluorone (PF) as a fluorescence probe has been developed. The fluorescence intensity of Mo(VI)-PF-beta-CD was diminished as the l-tyrosine was added, the fluorescence quenching value DeltaF=F(beta-CD-Mo-PF)-F(beta-CD-Mo-PF-l-Tyr) was enhanced in beta-CD and there was a linear relationship between the DeltaF and the concentration of l-Tyr. Under the optimal conditions, the linear range of calibration curve for the determination of l-tyrosine was 0.3-20.0microgmL(-1); the detection limit was 0.094microgmL(-1). NaOH (10%, w/v) is the best reagent of hydrolysis in sample preparation. The sensitized mechanism of beta-cyclodextrin was discussed. The method has been applied to the determination of l-tyrosine in spirulina and food samples with satisfactory results.