If you are working with microplates, prepare fresh H2O2 assay solution for each kinetic reading. For example, if you have 32 samples, prepare fresh for every 8 wells of the microplate, so you will prepare it 4 times in total. I wish you good work.
When performing a hydrogen peroxide antioxidant assay, handle H₂O₂ carefully as it is corrosive wear gloves and goggles. Always prepare fresh solutions and store them in dark bottles to prevent degradation. Use the correct concentration to avoid false results, and work in a ventilated area to prevent inhaling fumes.