Simultaneous determination of anthraquinones in Rhubarb by pressurized liquid extraction and capillary zone electrophoresis

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Abstract
Rhubarb, a well-known Chinese herbal medicine, is also used in Europe and other places of the world. Anthraquinones derivatives are thought to be the major active components. A pressurized liquid extraction (PLE) and capillary zone electrophoresis (CZE) separation were developed for simultaneous determination of five anthraquinones including aloe-emodin, emodin, chrysophanol, physcion, and rhein in Rhubarb. The effects of the experimental variables on PLE and CZE have been optimized. The optimum conditions of PLE were: solvent, methanol; temperature, 140°C; particle size, 0.13–0.2 mm; static extraction time, 5 min; pressure, 1500 psi; and one extraction. The best separation of the five anthraquinones could be obtained using 50 mM borate buffer (pH 8.2) containing 25% isopropyl alcohol and 25% acetontrile as modifier, while the separation voltage was 25 kV and the temperature was at 20°C. The method developed is accurate, simple, and reproducible, and could be used for quality control of Rhubarb and its medical preparations.