In Alcian blue staining at pH 1.0, sulfated mucosubstances appear as which color?

• A. Pale blue
• B. Pink
• C. Red
• D. Green

Answer: (A)

Alcian blue staining at very low pH tests selectivity for sulfated mucosubstances. At pH 1.0, carboxyl groups on mucopolysaccharides become protonated and lose charge, so they don’t bind the dye, while the sulfate groups remain negatively charged and attract Alcian blue. The dye therefore labels only the sulfated mucosubstances, producing a blue coloration that is typically described as pale blue. This allows differentiation from non-sulfated or carboxylated mucosubstances, which do not stain under these conditions.