First, different solutions like citrate buffer, 10% w/v urea, 12.5% w/v solution of sodium phenolate, and sodium hypochlorite solution were prepared. Citrate buffer (pH 6.7) was prepared by dissolve 24.09 g (M=0.0819) sodium citrate and 3.47 g citric acid (M= 0.0181) in 800 mL distilled water. Solution was well shaken for 5 min and more distilled water was added to make the volume of 1000 mL and adjust the pH of solution 6. The commercial sodium hypochlorite solution was a dilute solution with 50 mL d.H2O so that it contains 0.9% active chlorine. The solution was stable, allow to stand for 20 min until the maximum color was obtained. The optical density was measured within 60 min. According to an estimation, 1 mg of enzyme contains 45 IU enzyme units (0.01 g/1 mL) or 1 mg/1000. So, different enzyme standard curves were prepared by dissolving the enzyme stock solution into citrate buffer by following the Table .