Analysis of tryptophan at nmol l −1 level based on the fluorescence enhancement of terbium–gadolinium–tryptophan–sodium dodecyl benzene sulfonate system

Abstract

It is found that Tb 3+ can react with tryptophan (Trp) and sodium dodecyl benzene sulfonate (SDBS), and emits the intrinsic fluoresence of Tb 3+. The fluorescence intensity can be enhanced by La 3+, Gd 3+, Lu 3+, Sc 3+ and Y 3+, among which Gd 3+ has the greatest enhancement. This is a new co-luminescence system. The studies indicate that in the Tb–Gd–Trp–SDBS system, there is both Tb–Trp–SDBS and Gd–Trp–SDBS complexes, and they aggregate together and form a large congeries. The fluorescence enhancement of the Tb–Gd–Trp–SDBS system is considered to originate from intramolecular and intermolecular energy transfers, and the energy-insulating sheath effect of Gd–Trp–SDBS complex. Under the optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of Trp in the range from 4×10 −8 to 4×10 −5 mol l −1. The detection limit is 10 −9 mol l −1. The proposed method is one of the most sensitive fluoremetries of Trp.