Schiff reagent reduces the quinoid structure, producing Leucofuchsin. This statement is:

• A. True
• B. False
• C. Not applicable
• D. Both true and false

Answer: (A)

Schiff reagent works through a reversible redox change of the dye. The colored form of fuchsin has a quinoid structure; when Schiff reagent, which has been decolorized with sulfite, reacts, that chromophore is reduced to a colorless Leucofuchsin. In tissues, aldehyde groups generated by periodic acid (in the PAS component) react with this reduced form and reoxidize it back to the colored fuchsin, producing the characteristic magenta color. So the statement that Schiff reagent reduces the quinoid structure to produce Leucofuchsin is correct, because the Leucofuchsin is the reduced, colorless form of the dye that can be reoxidized to give color.