A novel nonaqueous capillary electrophoresis method for effective separation and simultaneous determination of aurantio-obtusin, emodin and rhein in semen cassiae and cassia seed tea

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Abstract
Anthraquinones (aurantio-obtusin, emodin and rhein) cannot be determined simultaneously using capillary zone electrophoresis because aurantio-obtusin has a low solubility in water. Therefore, a novel nonaqueous capillary electrophoresis (NACE) method with diode-array detection was developed for effective separation and simultaneous determination of the three anthraquinones. A BGE solution of 40 mM NaAc–40 mM NH4Ac–40 mM NaOH in methanol was used for separation of the three anthraquinones. The effects of ultrasonic extraction conditions and the NACE conditions on separation were investigated in detail. Under the optimized conditions, the analytes can be effectively separated in 7 min. The standard curves of the three anthraquinones showed good linearity, with correlation coefficients of r > 0.999. The limit of detection (LOD; signal to noise ratio (S/N) of 3) of aurantio-obtusin, emodin and rhein were 0.25, 0.12 and 0.19 μg mL−1, respectively. Their average intra- and inter-day analytical precisions (relative standard deviation) were less than 2.8% and 4.0%, respectively. The recoveries of the three spiked levels of aurantio-obtusin, emodin and rhein from semen cassiae and cassia seed tea samples were in the range of 86.6–106%. The proposed method provides the speediness, selectivity, sensitivity, linearity and accuracy as well as low reagent consumption necessary for simultaneous analysis of the test anthraquinones. The ultrasonic extraction–NACE method was used for the analysis of aurantio-obtusin, emodin and rhein in semen cassiae and cassia seed tea with satisfactory results, and could be applied for quality control of semen cassiae and cassia seed tea.

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