Determination of endogenous jasmonic acid in plant samples by liquid chromatography-electrochemical detection based on derivatization with dopamine

Jasmonic acid (JA), a type of plant hormone, is widely distributed in a variety of higher plants at very low concentrations, usually several nanograms per gram (ng g(-1)) fresh weight of the plant tissue. The determination of endogenous JA is challenging work. The typical electrochemical oxidation behavior of JA could only be achieved under extreme conditions such as strongly acidic medium (H2SO4) and high applied working potential (1.4-1.6 V), which cannot be used in the electrochemical detection for liquid chromatography (LC). To realize electrochemical detection for LC separation, a mild supporting electrolyte for JA oxidation is required, as the supporting electrolyte solution also serves as the mobile phase of LC. Thus, a novel electrochemical derivatization with dopamine (DA) has been developed and successfully applied to the analysis of endogenous JA in wintersweet flowers and rice florets by liquid chromatography coupled with electrochemical detection (HPLC-ECD). Under optimized experimental conditions including a detection potential of +0.90 V, and 0.04 mol L-1 acetate buffer solution (pH 5.07) : acetonitrile (67 : 33, v/v) as the mobile phase, the contents of JA in wintersweet flowers and rice florets were respectively determined to be 7.86 mu g g(-1) and 308 ng g(-1), consulting the linear relationship between the peak area of JA-DA derivatives and the standard JA concentration (1.0 x 10(-7) mol L (1) to 2.0 x 10 (5) mol L (1), R = 0.9986) with a detection limit of 5.0 x 10 (8) mol L (1) (S/N = 3). The results were consistent with those by LC-UV and LC-MS methods in our group, indicating that this novel pre-column electrochemical derivatization method is feasible.