1.2 Determination of Vitamin C in food
Vitamin C, L-ascorbic acid or L-ascorbate is an essential nutrient in humans. This is because we cannot synthesis the vitamin from glucose in the liver. It is thought that the absence of an enzyme l-gulonolactone oxidase from liver cells1 prevents humans from converting glucose into ascorbic acid. Ascorbic acid functions as an anti-oxidant in living organisms protecting the body against the effect of oxidative stress. Ascorbic acid is also important biologically as it is used as a cofactor in enzymatic reactions (no less than 8 reactions have been identified). These include the synthesis of collagen, a deficiency of which leads to the most notable disease of vitamin c loss, scurvy.
Ascorbic acid forms the part of many important physiological functions. These include the syntheses of collagen, neurotransmitters, tyrosine carnitine and metabolism of microsome2. But most importantly it is known for its antioxidant activity. When free radicals are present in cells as high levels they are thought to have an effect on cardiovascular disease, high blood pressure and chronic inflammatory diseases3. It is thought that ascorbic acid reacts with these free radicals preventing them from causing damage to cells.
How to measure the amount of Vitamin C in food
One way to measure the amount of vitamin C in our food is to use what is called a redox titration. The titration method takes advantage of the ability of Iodine to oxidise Vitamin C.
Iodine is relatively insoluble, but this can be improved by binding to iodide to form triiodide:
I2 + I- <--> I3-
Triiodide oxidizes vitamin C to form dehydroascorbic acid:
C6H8O6 + I3- + H2O --> C6H6O6 + 3I- + 2H+
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Quality of writing
One or two spaces between words are missing due to proof-reading errors. Other spelling, grammar and punctuation are all accurate.
Level of analysis
The background provided behind vitamin C as an introduction goes into very deep scientific and chemical depth which is great to be seen in an essay. The scientific terms used are presented to a high level of clearness and understanding of the topic. The risks evaluated by the student and the improvements suggested are quite average, and the student could have identified other risks associated with the experiment and better improvements. No-pre scientific tests are done which would increase the candidates mark to identify any confounding factors or biases and how the student would take this into account whilst setting out the experiment. The student could also improve by making a null hypothesis. The conclusion is adequate and the use of comparison against published values is good. The candidate could have used correct cm cubed terms, and could have improved their evaluation by calculating percentage errors in the equipment used and there are no possible improvements to the experiment suggested.
Response to question
Overall a good scientific essay. The introduction is fantastically written, but the conclusion and evaluation could use a lot more depth and improvements are suggested in point two. The response is written in a very clear and concise way.
