Ascorbic acid content of fruit juice Essay

OBJECTIVE To determine ascorbic acid content in a sample of fruit juice by using titration method with 0.001M 2,6-dichlorophenolindophenol, C12H7O2NCl2. INTRODUCTION image00.png Structure of Ascorbic acid Ascorbic acid, the chemical term for vitamin C, are found naturally in fruits and green vegetables. It is a dietary requirement for normal metabolism, formation of collagen, wound healing, and tissue repair. Ascorbic acid is often used as an antioxidant to help prevent free radical damage in the skin, builds resistance to infection, aids in the prevention treatment of the common cold, and aids in the absorption of iron. Yet, vitamin C cannot be synthesized by the body, and needs to be ingested. A lack of vitamin C can cause abnormalities of the spine, scurvy, and a reduction in the ability of the body to heal wounds. The determining factors as to whether organic substances can be determined in an aqueous medium depend primarily on the functional groups that characterise the redox properties. The determination of ascorbic acid content is based on the oxidation of ascorbic acid to dehydroascorbic acid: C6H8O6→ C6H6O6 + 2e- + 2H+ image01.png The redox potential depends on the pH and without adequate buffering the pH at the electrode surface can be displaced by the oxidation reaction of the ascorbic acid leading to peak broadening. Vitamin C is found in fruit drinks such as orange juice and also other sources like vegetables, liver and kidney meat. Vitamin C in food can be destroyed by cooking, leaching out from fruits and vegetable during washing, and being oxidized when expose to the air. Thus, food that rich in vitamin C needs to be stored and prepared well. PROCEDURE 1. Standardization of 0.001M 2, 6-dichlorophenolindophenol solution. 25.00mL aliquot of ascorbic acid solution was pipette into a 100mL conical flask. 0.001M 2, 6-dichlorophenolindophenol solution is titrated until a faint colour persisted for at least 15 seconds. The molarity of the dye solution is calculated by the result obtained. 2. Ascorbic acid concentration of fruit juice is determined. 5mL of fruit juice was pipette into a 100mL conical flask. 10mL of 5M acetic acid, 5mL of acetone (prevent interference of SO2) and 30mL of water was added, then the mixture was allowed to stand for 5 minutes and titrated with 2, 6-dichlorophenolindophenol solution. 3. CuSO4 and bubbling to air. 2 flasks is set up and filled with 25mL of fruit juice in each flask. 1mg of copper sulfate is added to one of the flasks and both are put to bubbled air for 20 minutes. The titration is repeated at the completion of the 20 minutes of air bubbling. DCPIP is a chemical compound used as a redox dye. This dye is blue in base (DCPIP-) and pink in acid (DCPIPH) and the pink form can be reduced by ascorbic acid to a colorless form (DCPIPH2). image03.png Titration with 0.001M 2,6- dichlorophenolindophenol solution Reaction 1: DCPIP- (blue) +H+→ DCPIPH (pink) Reaction 2: DCPIPH (pink) + Ascorbic acid → DCPIPH2 (clear) +Dehydroascorbate If a drop of blue DCPIP dye is added to a low pH solution (pH