HPLC Determination of Vitexin and Isovitexin from Crotalaria Sessiliflora L. with Response Surface Method to the Optimization of Conditions of Microwave Assisted Sample Extraction

The conditions for microwave assisted extraction of vitexin and isovitexin in Crotalaria sessiliflora L. with ethanol were optimized by applying the response surface method. Contents of vitexin and isovitexin in the extracts were determined by HPLC. Single factor testings were performed to select the conditions of extraction temperature, volume (mL) to mass (g) ratio of extracting solvent (C2H5OH) to sample and extraction time; and the conditions were optimized further by applying the central composite design principle at the mode of 3-factors and 3-levels, and the response surface analysis. The optimum extraction conditions found finally were as follow: ① extraction temperature of 152 ℃; ② ratio of C2H5OH (mL) to sample (g) of 44∶1; ③ extraction time of 6.6 min. Rate of extraction obtained under the optimum conditions attained to 253.3 μg·g-1 (for vitexin) and 236.9 μg·g-1 (for isovitexin), which were very close to the theoretical values. Values of recovery obtained by standard addition method were in the ranges of 97.0%-104% for vitexin and 96.0%-102% for isovitexin.