Abstract
Isomeric triterpenic acids of oleanolic acid (OA) and ursolic acid (UA) both have very low ultraviolet absorption and always exist in the same plant, so the separation and simultaneous determination of them have been a difficult task. In this study, a sensitive method combining dispersive liquid-liquid microextraction (DLLME) with HPLC-UV was developed for the extraction and determination of OA and UA in traditional Chinese medicinal herbs (CMHs). Variables influencing DLLME such as type and volume of extraction solvent, volume of dispersive solvent, ionic strength, aqueous phase pH, extraction time, centrifugation speed and time, and sample volume were investigated and optimized. Under the optimum conditions, both OA and UA attained favorable extraction efficiencies with enrichment factors 1378 and 933, respectively. The linear dynamic ranges of 0.07 - 30.4 μg?mL–1 for OA and 0.08 - 33.6 μg?mL–1 for UA were obtained with square correlation coefficients of 0.9963. The detection limits of OA and UA were both 0.02 μg?mL–1. The method recoveries ranged between 88.2% - 116.2% for OA and 85.7% - 108.2% for UA with the RSDs (n = 5) lower than 8.6%. The proposed method was successfully applied to concentrate and simultaneously determine these two triterpenic acids in Hedyotis diffusa and Eriobotrya japonica samples.
Highlights
Oleanolic acid (OA) and ursolic acid (UA) are isomeric triterpenic acids with only one methyl’s position difference between them (Figure 1)
A sensitive method combining dispersive liquid-liquid microextraction (DLLME) with HPLC-UV was developed for the extraction and determination of oleanolic acid (OA) and UA in traditional Chinese medicinal herbs (CMHs)
The separation and determination of the two components in plants are usually performed by using chromatographic method, such as Micellar Electrokinetic Capillary Chromatography (MECC) [14], Capillary Zone Electophoresis (CZE) [15], direct HPLC-UV detection [16] and HPLC-DAD [17], pre-column derivatization HPLC [18] and Iodine Derivatization High Performance Thin-Layer Chromatography (IDHPTLC) [19]
Summary
Oleanolic acid (OA) and ursolic acid (UA) are isomeric triterpenic acids with only one methyl’s position difference between them (Figure 1). The separation and determination of the two components in plants are usually performed by using chromatographic method, such as Micellar Electrokinetic Capillary Chromatography (MECC) [14], Capillary Zone Electophoresis (CZE) [15], direct HPLC-UV detection [16] and HPLC-DAD [17], pre-column derivatization HPLC (pre-CD-HPLC) [18] and Iodine Derivatization High Performance Thin-Layer Chromatography (IDHPTLC) [19]. System including disperser solvent, extraction solvent and aqueous sample containing interest analytes [21] This new sample-preparation technique, that set extraction, purification and concentration of the target analytes in one step, has the following characteristics: simplicity of operation; high enrichment factor; low organic solvent consumption (generally a few to dozens of microliters); low labor cost and cheap equipment. It is found that DLLME coupled with HPLC is a simple, fast, sensitive, efficient and green method for the simultaneous analysis of OA and UA in CMH samples
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