A New HPLC-UV Method Using Hydrolyzation with Sodium Hydroxide for Quantitation of Trans-p-Hydroxycinnamic Acid and Total Trans-p-Hydroxycinnamic Acid Esters in the Leaves of Ligustrum robustum

Trans-p-hydroxycinnamic acid and its esters in the leaves ofLigustrum robustummight be a new resource to prevent diabetes and its complications. In the present study, a new HPLC-UV method using hydrolyzation with sodium hydroxide for quantitation oftrans-p-hydroxycinnamic acid and totaltrans-p-hydroxycinnamic acid esters in the leaves ofL. robustumwas developed, since it was difficult and troublesome to analyze no less than 34trans-p-hydroxycinnamic acid esters by usual HPLC. The extract ofL. robustumwas hydrolyzed with sodium hydroxide at 80 °C for 2 h, and then, hydrochloride was added. HPLC analysis was performed in reverse phase mode using a C-18 column, eluting with methanol-0.1% acetic acid aqueous solution (40:60,v/v) in isocratic mode at a flow rate of 1.0 mL·min−1and detecting at 310 nm. The linear range fortrans-p-hydroxycinnamic acid was 11.0–352.0 μg·mL−1(r2= 1.000). The limit of detection and limit of quantification were 2.00 and 6.07 μg·mL−1, respectively. The relative standard deviations of intra-day and inter-day variabilities fortrans-p-hydroxycinnamic acid were less than 2%. The percentage recovery oftrans-p-hydroxycinnamic acid was 103.3% ± 1.1%. It is the first HPLC method using hydrolyzation for quantification of many carboxylic esters. Finally, the method was used successfully to determinetrans-p-hydroxycinnamic acid and totaltrans-p-hydroxycinnamic acid esters in various extracts of the leaves ofL. robustum. The 60–70% ethanol extracts ofL. robustumshowed the highest contents of freetrans-p-hydroxycinnamic acid (3.96–3.99 mg·g−1), and the 50–80% ethanol extracts ofL. robustumdisplayed the highest contents of totaltrans-p-hydroxycinnamic acid esters (202.6–210.6 mg·g−1). The method can be applied also to the quality control of the products ofL. robustum.Keywords:trans-p-hydroxycinnamic acid;esters;Ligustrum robustum;HPLC-UV;hydrolyzation;sodium hydroxide;quantification