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

It is found that Tb3+ can react with tryptophan (Trp) and sodium dodecyl benzene sulfonate (SDBS), and emits the intrinsic fluoresence of Tb3+. The fluorescence intensity can be enhanced by La3+, Gd3+, Lu3+, Sc3+ and Y3+, among which Gd3+ 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. 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.