Measurement of Vitamin C

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Nutritional diseases were once the number one cause of death only a century ago, but rarely affect our lives today. The complete lack of vitamin C (ascorbic acid) characterized by dark purple spots on the skin and rotting gums, a disease called scurvy, took the lives of many sailors up until the mid 1800s when the prevention was discovered. Consequently, British sailors became referred to as ‘limeys’ because of their daily habit of eating limes to maintain their vitamin C levels. Citrus fruits and green plants synthesize a very high concentration of ascorbic acid, and other plants and most all animals can produce some amount as well, except humans. We must rely on our dietary intake to maintain healthy levels of this nutrient.

The recommended amount of vitamin C ranges from about 60mg up to 3g per day, depending on the physician and the individual’s needs, but many products on the market are supplemented with ascorbic acid to ensure our daily requirements can be met. While scurvy is no longer a predominant threat to our health, deficiency of vitamin C can still cause a few complications affecting our joints and a weakness getting over the flu. Therefore, it is imperative that vitamin C concentrations can be quantified in what we consume and its presence in our bodies.

Ascorbic acid can be analyzed using titration techniques with iodine, 2,4-dinitrophyenylhydarzine, a redox indicator, or N-Bromosuccinimide (NBS), but caution must be used with temperature because ascorbic acid in the oxidized form, dehydroascorbic acid, is unstable. Both forms are biologically active, but dehydroascorbic acid has no affect with scurvy.

N-Bromosuccinimide (NBS) readily oxidizes ascorbic acid before other interferences can react, enabling reliable measures of ascorbic acid content by titration. The addition of potassium iodide and starch to create a titration endpoint marker can therefore be done without...
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