Complete lack of ascorbic acid (a.k.a Vitamin C) in the diets of humans and other primates leads to a classic nutritional disease, scurvy. This disease was widespread in Europe during the fifteenth and sixteenth centuries, but it is rare today. Ascorbic acid is widely distributed in nature, but it occurs in extremely high concentrations in citrus and green plants such as green peppers and spinach. Ascorbic acid can be synthesized by all plants and animals, with the exception of humans, other primates, and guinea pigs. Therefore, vitamin C must be present in our dietary substances. The fundamental role of ascorbic acid in metabolic processes is not very well understood. There is some evidence that it may be involved in metabolic hydroxylation reactions of tyrosine, proline, and some steroid hormones, and in the cleavage-oxidation of homogentisic acid. Its function in these metabolic processes appears to be related to the ability of vitamin C to act as a reducing agent.
The adult Recommended Daily Allowance f vitamin C is 70 mg per day. Some scientists and physicians have suggested doses up to 1 to 3 grams per day in order to help resist the common cold. Deficiency of vitamin C results in swollen joint, abnormal development and maintenance of tissue structures, and eventually scurvy. Determination of vitamin C in biological fluids such as bolld and urine is difficult because only small amounts of the vitamin are present and many interfering reducing agents are present. Substances containing sulfhydryl groups, sulfite, and thisosufate are common in biological fluids and react with DCIP, but much more slowly than ascorbic acid. The interference by sulfhydryl is often minimized by the addition of p-cholormercuribenzoic acid.
Materials and Supplies
Apple Juice Metaphosphoric acid/ Acetic acid solution 4% Unknown ascorbic acid in metaphosphoric acid/acetic acid solution, .5mg/ml 2,6 dicholorphenolindophenol solution in water
Ascorbic acid oxidase, lyophilized water
Standard Ascorbic Acid Solution
Fill a microburet with DCIP solution. Using a pipet, transfer 1.0 ml of the ascorbic acid standard solution to a 50 ml Erlenmeyer flask containing 5 ml of 4% metaphosphoric acid solution. Read and record the initial reading on the buret. Titrate by rapid, dropwise addition of DCIP from the buret while mixing the contents of the flask. Add DCIP solution until a distinct rose-pink color persists for 15-20 seconds. Record the final reading on the buret. Repeat this procedure twice more, each time with a fresh 1.0 ml sample of ascorbic acid standard. In a similar fashion, titrate three blanks, each containing 5.o ml of 4% metaphosphoric acid and 1.0 ml of water. Average the results for each series of measurement. Do the same for the apple juice sample, and the two unknowns.
The apple juice company claims that their apple juice contains 40% of the recommended daily allowance for Vitamin C. However, I have found that the company in actuality only contains less than 3%. Is this an honest mistake or is this yet another example of corporate dishonesty to the consumer. There may have been error in the experimental procedures. Many people use the lab and the equipment and the chemicals. Contamination of the chemicals used may have easily occurred. There may have been mistakes in pipetting and transferring.