Abstract: The present invention relates to a method for determining the concentration of oxygen-centered free radicals in a sample. The method uses a chromogen chosen from the following group: with R1, R2, R3, and R4 being —CH2CH3, —CH3, —H, or —X, with X being a halogen. The method includes combining a working reagent having a selected chromogen and a buffer with a sample containing free radicals. Quantitative determination of the concentration of the free radicals in the sample is then determined, based on the chromogenic reaction which takes place.