The buffer stock solution consisted of 3.025 g tris-(hydroxymethyl)-aminomethane, 2.9 g maleic acid, 3.5 g citric acid, 1.57 g boric acid, 1 M sodium hydroxide (NaOH) solution (122 ml) and distilled water added to give a final volume of 250 ml.
Take 50 ml of this solution, adjust pH you need in enzyme assay, add water (whole 250ml)