Phosphate-Citrate Buffer Tablets with Urea Hydrogen Peroxide may be used as a peroxidase substrate buffer for ELISA with the H2O2included.Reconstitution: One tablet dissolved in 10 mL of deionized water yields a 0.05 M phosphate-citrate buffer, containing 0.014% H2O2, pH 5.0 at 25 °C.