BioChain's peroxide assay kit is a simple, direct and automation-ready assay for measuring peroxide concentration in biological samples without any pretreatment. The improved method utilizes the chromogenic Fe3+-xylenol orange reaction, in which a purple complex is formed when Fe2+ provided in the reagent is oxidized to Fe3+ by peroxides present in the sample. The intensity of the color, measured at 540-610nm, is an accurate measure of the peroxide level in the sample. The optimized formulation substantially reduces interference by substances in the raw samples.