Simultaneous determination of Aloe-emodin and Rhein by synchronous fluorescence spectroscopy.

A simple sensitive and quick assay to simultaneously determine Aloe-emodin (AE) and Rhein (RH) has been described based on their natural fluorescence. Due to their similar molecule structures, it is difficult to analysis and determine their contents by conventional fluorometry. Overlapping of fluorescence spectra was resolved by using synchronous fluorometry. The synchronous spectrum, maintaining a constant difference of Deltalambda=25 nm between the emission and excitation wavelengths, has been selected as optimum to perform the determination. This method was applied to the simultaneous determination of AE and RH in simulated mixtures. Analytical recoveries range from 94.5 to 105.5% for AE and from 98.7 to 107.5% for RH. At the same time, the content of AE abstracted from Cassitora L. was successfully analyzed. The results were satisfactory.