Fluorescence Properties of Magnoflorine and Its Application in Analysis of Traditional Chinese Medicine

Fluorescence and absorption spectra of magnoflorine (MAG) were studied. The effects of environmental factors such as pH on fluorescence and absorbance were investigated , and the relationship between spectral properties and molecular structure was revealed. Three fluorescent peaks appeared in the three-dimensional (3D) fluorescence spectra of the aqueous solution of MAG, with excitation wavelengths (lambda(ex)) of 230 , 275 and 315 nm , and the same emission wavelength (lambda(em)) of 420 nm. As the pH of the solution increased , the fluorescence peak in the excitation spectrum red-shifted and an equal fluorescence point appeared, and the absorption peak in the absorption spectrum also red-shifted and an isosbestic point formed , indicating that proton ionization occurred in one hydroxyl group in the MAG molecule. The proton ionization constant (pK(a) = 4. 77) of MAG was determined by a pH-absorption method. Using L-tryptophan as a reference, the fluorescence quantum yield of the aqueous solution of MAG was determined to be Y=0. 19. The characteristic fluorescence peaks of MAG appeared in the 3D fluorescence spectra of various Chinese herbal medicines. Using methanol-water mixed solvent containing 60% methanol, the extract of Sinomenium acutum (Qingfengteng) was prepared and diluted with water, then 3D fluorescence spectra were obtained. It was observed that the fluorescence peak at lambda e(x)/lambda(em) = 315 nm/420 nm in the spectrum of the Qingfengteng neutral aqueous solution was not affected by the coexisting components. Based on this, a method for the determination of MAG in Qingfengteng was established. In the range of 0. 04 -1. 25 mu g/mL , the regression equation 14 fluorescence intensity (I-F) and MAG concentration (c) was I-F = 6146. 8c + 24.4 , ( R = 0.999 , n = 11 ) , with a detection limit of 0. 52 ng/mL. The content of MAG in the Qingfengteng reference material was determined to be 0.63% by the method , and the recoveries were 101.2%-102.7% . The content of MAG (0. 61% ) in the same sample was also determined by LC-MS/MS method, which was consistent with the fluorescence method.