Hydrogen peroxide is a central reactive oxygen species produced by enzymes such as SOD and XOD and degraded by CAT and POD. It functions both as an oxidant causing biomolecular damage and as a signaling molecule in oxidative stress responses. H2O2 reacts with titanium sulfate to form a yellow peroxytitanium complex with absorbance at 415 nm. The absorbance correlates with H2O2 concentration.