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In this study, flavonoids were extracted using accelerated solvent extraction (ASE) with 80% aqueous methanol. A high-performance liquid chromatography equipped with photodiode array detection and coupled with an electrospray ionization tandem mass spectrometry (HPLC–PDA–ESI/MSn) method has been developed for rapid identification and quantification of flavonoids in the plant extract of Rheum palmatum L. (RPL) seeds from Qinghai. Ten flavonoids from methanolic extract of RPL seeds were screened, of which epicatechin, myricetin, hyperoside, quercitrin and quercetin were identified and quantitatively analyzed for the first time. The absorbance was monitored at 280 nm for epicatechin and 360 nm for other four flavonoids. It was found that the calibration curves for all five analytes showed a good linearity (r2 > 0.999) within the test range and the data of the limit of detection (LOD) and limit of quantification (LOQ) for all investigated compounds were less than 2.98 μg mL−1 based on PDA. The relative standard deviation (R.S.D) values of the intra- and inter-day precisions were 0.98% and 1.65%, respectively. The range of mean recoveries of the five components was 91.3–93.9%, and the R.S.D was 1.3–2.9%. It was also found that the content of quercitrin is the highest in RPL seeds while the contents of epicatechin and myricetin are relatively lower. In addition, the validation procedure confirmed that this method was suitable for providing quality control evaluation of RPL seeds to ensure the therapeutic benefits. Keywords: Seeds of Rheum palmatum L., Identification, Quantification, Flavonoids, Accelerated solvent extraction, HPLC–PDA–ESI/MSn

Inula racemose Hook.f. ( I . racemosa ) is a traditional herbal medicine with strong anti-fungal and anti-inflammation activity while alantolactone (AL) and isoalantolactone (IAL) are the major active compounds of this plant. The aim of this paper was obtaining AL and IAL from the radix of I . racemosa by supercritical fluid extraction (SFE) which was optimized by response surface methodology (RSM). Our results showed that, the optimal conditions for maximum extraction efficiency were as follows: pressure 20 MPa, extraction temperature 50 °C, carbon dioxide (CO 2 ) flow rate of 17.0 × 10 −5 kg/s and extraction time of 40 min. Subsequently, an efficient freezing method was developed for purification of AL and IAL in the crude extract obtained from SFE. After purification by freezing, the total content of the target compounds was greatly improved by 30.7%. The results demonstrate that SFE coupled with freezing would be a powerful technique for extraction and purification of AL and IAL from the radix of I . racemosa .

Limonium aureum (Linn.) is a traditional Chinese medicine with strong antioxidant activity. To search for antioxidants in L. aureum , an optimized, on-line high performance liquid chromatography (HPLC) method with DPPH (1,1-diphenyl-2-picrylhydrazyl) for the detection of radical scavenging ability was developed. Response surface methodology (RSM) was used to determine the best combination of experimental conditions, such as DPPH concentration, DPPH velocity and the reaction tank length. The optimized method uses a DPPH concentration of 25.0 μg/mL, DPPH velocity of 0.45 mL/min and a 15.0 m long reaction tank. The highly sensitive, optimized method can not only be used for the detection of antioxidants in plants, but can also be coupled with mass spectrometry (MS) to obtain the mass-to-charge ratios of chemical species corresponding to the different peaks in the HPLC profiles. Seven antioxidants were identified in L. aureum using the optimized method, including myricetin-3- O -β- d -(6”- O -galloyl)-glucopyranoside, myricetin-3- O -glucoside, myricitrin, eriodictyol-7- O -glucoside, myricetin, eriodictyol and homoeridictyol.