New luminescent probe based on Europium (III) complex for determination of curcumin
A spectrofluorimetric method is developed for the determination of curcumin (CC) in pharmaceuticals and food, based on its quenching effect on the fluorescence intensity of a complex of Eu3+ ions with batophenantrolin (BPhen) as a fluorescent probe. The optimum conditions for the determination of CC were investigated. presence of CC have been studied. The composition of the Eu3+-BPhen complex with stoichiometric ratio (1:1) (metal: ligand) was determined spectrofluorimetrically in aqueous solution at pH=7,5 by the application of Bent-French's method. The fluorescence intensity of the Eu(III)-BPhen complex in the spectra excitation and emission is decreased with increasing of CC concentration owing to formation of Eu(III)-BPhen-CC complex with stoichiometric ratio (1:1:1). It was established that the fluorescence lifetime of the Eu(III)-BPhen complex at λem = 615 nm is about 300 μs does not change upon increasing quencher concentration. Thus, the quenching effect on the luminescence of the Eu (III)-Bphen complex by CC is occurred via static mechanism. The CC was remarkably quenched the luminescence intensity of the the Eu(III)-BPhen probe. Under optimal conditions, the quenching of luminescence intensity was found to be proportional to the concentration of CC in the range from 2 to 100 ng/ml. The detection limit was calculated according to the 3σ-criterion is equal to 0,7 ng/ml. Fluorescence quenching is described using the Stern-Volmer equation. The Stern-Volmer quenching constant KSV = 0,045 ml·ng-1. KSV value indicates that molecules of curcumim effectively quench the luminescence of the Eu(III)-BPhen complex. The effect of luminescence quenching of the Eu(III)-BPhen complex was used to developing the procedure for determining of CC (CEu = 10-4 mol/l, CBPhen = 10-4 mol/l, in aqueous solutions at pH = 7,5-8,0, λex = 320 nm, λem = 615 nm). A spectrofluorimetric method was applied to determination of CC in curcumin extract powder (NATUREX OF3489, France).