Assay of ascorbic acid Hawzhin A.Salih MSc.student in Medicinal chemistry

What is ascorbic acid? Ascorbic Acid is a naturally occurring and water soluble vitamin. It can either be a white solid (pure sample) or appear yellowish (impure sample). It dissolves well in water to give mildly acidic solution. The main sources of vitamin C are citrus fruits, strawberries, peppers, tomatoes, cabbage, and spinach. M.formula: C6H8O6 M.wt: 176g/mol

Therapeutic uses of vitamin C It is used in the prevention and treatment of Scurvey. It acts as anti-wrinkle agent due to participating in collagen biosynthesis. Improving intestinal absorption of metal iron. Prevention of cancer due to its antioxidant property. Immune stimulating effect of vitamin c gives its role as active ingredient in common cold preparations.

Analysis methods There are numerous methods for the determination of vitamin C in a variety of natural samples, biological fluids and pharmaceutical formulations: HPLC(High Performance Liquid Chromatography) Spectroscopic methods Enzymatic assay Titration

Aim of experiment Determination of the weight of ascorbic acid in a tablet of vitamin c by iodometric redox titration.

Types of titration reaction Acid-base reaction Oxidation-reduction or redox reaction. Precipitation reaction. Complex formation reaction

Chemical reaction

Chemicals and glassware Iodine solution 0.005M Vitamin c tablet Starch as indicator H2SO4 1M Deionized water Glasswares: Conical flask 250ml,burette,stand and clamp, graduated cyclinder,white paper.

procedure grind a vitamin c tablet by mortar and pestle, then dissolve it in 250ml D.W. Pour 35 ml of 0.005M of iodine solution into the burette to mark. take 5ml of the sample solution and poured into a conical flask 250ml. add 25ml of 1M H2SO4. 100ml of D.W also added. Finally, add1.5ml of soluble starch as PH indicator followed by thorough shaking. Titrate until a blue– violet or green-violet color is obtained.

Calculation of weight of ascorbic acid/tablet No.of mole analyte(A.A) = no.of mole titrant(iodine) = M*V(L) M=0.0015 mol/L; V= predicted volume from titration So from this; no.of mole of A.A can be calculated in 5ml solution. In 250ml(original sample),no.of mole A.A=the previous value multiplied by 50. Mole=wt/m.wt; thus the weight of the vitamin c in the tablet can be calculated in gram.