A new test method for the evaluation of total antioxidant activity of herbal products.

A new test method for measuring the antioxidant power of herbal products, based on solid-phase spectrophotometry using tetrabenzo-[b,f,j,n][1,5,9,13]-tetraazacyclohexadecine-Cu(II) complex immobilized on silica gel, is proposed. The absorbance of the modified sorbent (lambda(max) = 712 nm) increases proportionally to the total antioxidant activity of the sample solution. The method represents an attractive alternative to the mostly used radical scavenging capacity assays, because they generally require complex long-lasting stages to be carried out. The proposed test method is simple ("drop and measure" procedure is applied), rapid (10 min/sample), requires only the monitoring of time and absorbance, and provides good statistical parameters (s(r)<or= 0.2). The method was approved in the analysis of the most popular herbal beverages (black and green teas) and drugs (Echinacea products). The results obtained were compared with the content of total flavonoids and tannins of teas and total caffeic acid derivatives of Echinacea, determined spectrophotometrically.