Abstract: The aims of this study were to explore method for the on-line detection of alkaloids with antioxidant activity from the stems of Dendrobium officinale Kimura et Migo by HPLC-UV-CL system,and to provide references on researching the potential material base of D.officinale and on quick discovery of antioxidants from traditional Chinese medicine.The on-line HPLC-UV-CL analysis with Luminol-perhydrol chemiluminescence system as the donor of hydroxyl radicals was applied to evaluate the antioxidant activity of the constituents of the total alkaloid extract from D.officinale. The alkaloids were discerned by alkaloid knock out using phosphomolybdic acid and iodine-potassium iodide as precipitation reagent.It was resulted that total five kinds of D.officinale alkaloids (HPLC peak 5,7,8,10 and 11) were detected and four of them showed remarkable hydroxyl-radical-cleaning activity with the calibration clearance values of 3.8%,4.0%,5.2% and 2.6%,respectively,determined by the established on-line HPLC-UV-CL method.The on-line HPLC-UV-CL system can be used to evaluate the antioxidant activity of D.officinale alkaloids and our study might provide experimental data for the quality control and the following directional isolation of antioxidant active components of D.officinale.

Key words: Dendrobium officinale, knock out by precipitation, HPLC-UV-CL, alkaloids