[Selective enrichment of iridoid glucosides in Hedyotis diffusa Willd. by tandem solid phase extraction]

A method for selective enrichment of iridoid glucosides in Hedyotis diffusa Willd. by tandem solid phase extraction (SPE) was developed. Oligo(ethylene glycol) (OEG) is a novel type of separation material made in this laboratory. The differences of the surface chemical structures between OEG material and ODS material resulted in their different retention capabilities for iridoid glucosides. Based on the differences, an OEG-ODS solid phase extraction method was designed for selective enrichment of iridoid glucosides. The water extract (150.28 mg) of Hedyotis diffusa Willd. was precipitated by ethanol, and an aliquot (27.03 mg) of the product from the supernatant solution was loaded onto an OEG cartridge and rinsed by 5 mL water. Then, the rinsing solution was loaded onto an ODS cartridge. After it was washed by 5 mL water and eluted by 5 mL methanol, 4.01 mg final product was obtained from the methanol eluent. All the products were characterized by ultra performance liquid chromatography (UPLC), and 14 representative peaks of iridoid glucosides were found. The enrichment results were proved effective by directly comparing the chromatograms each step. To further characterize the enrichment efficiency, the changes of the peak area of iridoid glucosides were investigated. The results showed that the content of 14 iridoid glucosides in the final product reached 6.10 times its original proportion in water extraction product and their recovery was 50.1% on average. Therefore, the iridoid glucosides can be enriched by the tandem solid phase extraction method from water extracting-ethanol precipitating solution of Hedyotis diffusa Willd. with a good selectivity and an acceptable recovery. The proposed method has the advantages of high enrichment efficiency and simple operation.