Simultaneous determination of five components in Eucommia ulmoides leaves by HPLC based on deep eutectic solvent and microwave-assisted extraction

To explore the reasons for the uneven quality of commercial Eucommia ulmoides leaves, an HPLC method based on deep eutectic solvent (DES) and microwave-assisted extraction (MAE) was developed to determine the contents of eucommiol, aucubin, geniposidic acid, chlorogenic acid and asperuloside. A DES composed of choline chloride and urea (molar ratio 1∶2) with water content of 40% exhibited the highest efficacy. MAE was selected and the optimized conditions were microwave power of 70 W and extraction time of 15 s. The contents of five compounds in green leaves were significantly higher than those in yellow-brown leaves. Part of yellow-brown leaves even lacked aucubin, geniposidic acid and asperuloside. The contents of five compounds were the highest in the leaves treated with sun-drying and low-temperature drying, followed by the deactivated enzymes leaves and shade-drying leaves. The content of each chemical component, especially iridoids, decreased significantly in room temperature. However, the contents of the compounds decreased slowly in low temperature. There was a significant difference in the quality of commercially available green and yellow-brown Eucommia ulmoides leaves, which may be related to the drying and storage methods.