The peroxide concentration is determined by reaction of the biological peroxides with peroxidase and a subsequent colour reaction using TMB as substrate. After addition of a stop solution, the coloured liquid is measured photometrically at 450 nm. A calibrator is used to calculate the concentration of circulating biological peroxides in the sample (one-point calibration). Sample Types: serum, plasma, cell culture. Range: 7 - 600 μmol/l. Sensitivity: 7 μmol/l. Time: 15 minutes ? Cells and tissues are sensitive to oxidative stress, caused by the formation of free radicals. If not deactivated by antioxidants, organic peroxides and hydroperoxides are the first reaction products between cellular constituents and free radicals or other reactive oxygen derivates.