Far infrared-assisted extraction followed by MEKC for the simultaneous determination of flavones and phenolic acids in the leaves of Rhododendron mucronulatum Turcz.

A method based on micellar electrokinetic chromatography with amperometric detection and far infrared-assisted extraction has been developed for the simultaneous determination of two flavones (rutin and farrerol) and three phenolic acids (syringic acid, vanillic acid, and 4-hydroxybenzoic acid) in the dried leaves of Rhododendron mucronulatum Turcz., a commonly used traditional Chinese medicine. The effects of some important factors such as the voltage applied on the infrared generator, irradiation time, the concentration of borate and sodium dodecylsulfate (SDS), separation voltage, and detection potential were investigated to acquire the optimum conditions. The detection electrode was a 300-μm diameter carbon disc electrode. The five analytes could be well separated within 8 min in a 40 cm-long capillary at a separation voltage of 12 kV in a 50 mM borate buffer (pH 9.2) containing 50 mM SDS. The relationship between peak current and analyte concentration was linear over about three orders of magnitude with the detection limits (S/N=3) ranging from 0.20 to 0.46 μM. The results indicated that far infrared irradiations significantly enhanced the extraction efficiency. The extraction time was substantially reduced to 6 min compared with 3 h for conventional hot solvent extraction.