Fluorescence Analysis Of Chinese Herbal Medicine-Cortex Fraxini And Its Effective Components

Fluorescence spectra, absorption spectra and protonation properties of Chinese herbal medicine—Cortex Fraxini and its effective components—aesculin and aesculetin have been studied in this thesis. Based on the spectroscopic properties of aesculin and aesculetin at different pH values of their water solutions, a fluorescence method for the determination of aesculin and aesculetin in Cortex Fraxini was developed.The main contents of the thesis are as follows:1. Fluorescence spectra and UV absorption spectra of aesculin were studied. The influence of acidity on fluorescence and absorption spectra were investigated. Using quinine bisulphate as a reference, fluorescence quantum yield of aesculin in the condition of pH=4.96 was determined to be 0.76 at excitation wavelength 335nm, and in pH=9.40 was 0.80 at 375nm. The ionization constant of aesculin was determined to be pKa= 6.82 by UV absorption method.2. Fluorescence spectra and UV absorption spectra of aesculetin were studied. The influence of acidity and concentration on fluorescence and absorption spectra were investigated. Using quinine bisulphate as a reference, fluorescence quantum yield of aesculetin in the condition of pH=9.32 was determined to be 0.13 at excitation wavelength 365nm. The ionization constant of aesculetin was determined to be pKa1= 5.31 by UV absorption method.3. According to the fluorescence differences of aesculin and aesculetin at different pH values, a fluorescence method was developed for the determination of aesculin and aesculetin in Cortex Fraxini. First, at the condition of pH≈3, the quantity of aesculin was determined by choosing excitation wavelength 335nm and emission wavelength 455nm. Second, at the condition of pH≈9, the total fluorescence intensity of aesculin and aesculetin at wavelengthλex/λem=371nm/459nm was measured, and then the quantity of aesculin can be calculated. By using standard addition method and standard curve method, the quantity of aesculin in Cortex Fraxini was determined to be 0.10% and the aesculetin was 0.36%, respectively. The 3D fluorescence technique was also used to identify Cortex Fraxini from similar Chinese medicine Albizia Julibrissin.