FSCN 4613 Lecture Notes - Lecture 7: Triiodide, Potassium Iodide, Quinoxaline
23 Mar 2020
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Useful and most practical measurement of vitamin c. Plasma levels are rapidly affected by changes in dietary intake; 30-40 days before signs of scurvy appear. Plasma ascorbic acid does respond to intake of ascorbic acid. Vitamin c exists as both reduced (ascorbate) and oxidized (dehydroascorbate) forms in plasma. Our procedure will measure both forms using a fluorometric method. Oxidation of ascorbic acid to dehydroascorbic acid. An iodine solution is made, containing a mixture of iodine (i2) and potassium iodide (ki), which results in the formation of triiodide. The triiodide oxidizes ascorbic acid to dehydroascorbic acid. Removal of excess iodine by addition of sodium thiosulfate. By this reaction, the iodine is no longer an oxidizing agent, and will not interfere with subsequent reactions. Reaction of dehydroascorbic acid with o-phenylenediamine to form the fluorescent compound quinoxaline. Compounds present in plasma that naturally fluoresce. Must correct for these to get accurate measure of plasma fluorescence.
