Analysis of tryptophan at nmoll(-1) level based on the fluorescence enhancement of terbium-gadolinium-tryptophan-sodium dodecyl benzene sulfonate system.

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 4x10(-8) to 4x10(-5)moll(-1). The detection limit is 10(-9)moll(-1). The proposed method is one of the most sensitive fluoremetries of Trp.