High-performance liquid chromatography with post-column 2,2'-diphenyl-1-picrylhydrazyl radical scavenging assay: methodological considerations and application to complex samples.

An improved post-column 2,2'-diphenyl-1-picrylhydrazyl (DPPH*) radical scavenging assay for the screening of antioxidants in complex matrices was developed. Experimental parameters believed to be influential to DPPH* response were studied in a univariate approach. Optimum conditions were found to be: 5 x 10(-5) M DPPH* reagent prepared in a 75% methanol: 25% 40 mM citric acid-sodium citrate buffer (pH 6) solution, degassed with nitrogen; reaction coil of 2 m x 0.25 mm i.d. PEEK tubing; detection at 521 nm; analysis at room temperature. The analytical utility of this protocol was evaluated by screening for antioxidants in thyme and green tea, in comparison with two commonly employed methodologies.