The oxidizing agent (NBS) was standardized by taking an aliquot of 10 mL of a standard solution of ascorbic acid (0.2 mg mL1), which is placed in a 250 mL Erlenmeyer flask containing 2 mL of a solution of KI (4 g/L), 0.8 mL of a solution of acetic acid (10 g/L), drops of a solution of starch (1 g/L) as indicator and 12 mL of distilled water, then titrated with a solution of NBS (0.2 g/L).