An on-line HPLC method for detection of radical scavenging compounds in complex mixtures

A rapid on-line method for screening of complex mixtures for radical scavenging components was developed using a methanolic solution of 2,2'-diphenyl-1-picrylhydrazyl (DPPH) stable free radical. The HPLC-separated analytes react postcolumn with the DPPH solution, and the induced bleaching is detected as a negative peak by an absorbance detector at 517 nm. An optimized instrumental setup is presented. The method is suitable for both isocratic and gradient HPLC runs with mobile-phase compositions ranging from 10 to 90% organic solvent in water or buffer (pH 3-6). The method is simple, has a broad applicability, and uses common instruments, inexpensive and stable reagents, and a time-saving and nonlaborious experimental protocol. It can also be used for quantitative analysis. The method was applied to several pure natural antioxidants and plant extracts. The limits of detection were 0.33-94 mu g/mL, depending on the compound tested.