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 of Ligustrum robustum might 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 of trans - p -hydroxycinnamic acid and total trans - p -hydroxycinnamic acid esters in the leaves of L. robustum was developed, since it was difficult and troublesome to analyze no less than 34 trans - p -hydroxycinnamic acid esters by usual HPLC. The extract of L. robustum was 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 -1 and detecting at 310 nm. The linear range for trans - p -hydroxycinnamic acid was 11.0-352.0 μg·mL -1 ( r 2 = 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 for trans - p -hydroxycinnamic acid were less than 2%. The percentage recovery of trans - 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 determine trans - p -hydroxycinnamic acid and total trans - p -hydroxycinnamic acid esters in various extracts of the leaves of L. robustum . The 60-70% ethanol extracts of L. robustum showed the highest contents of free trans - p -hydroxycinnamic acid (3.96-3.99 mg·g -1 ), and the 50-80% ethanol extracts of L. robustum displayed the highest contents of total trans - p -hydroxycinnamic acid esters (202.6-210.6 mg·g -1 ). The method can be applied also to the quality control of the products of L. robustum .