Which Alcian Blue pH demonstrates carboxylated acid mucopolysaccharides?

• A. pH 1.0
• B. pH 2.5
• C. pH 3.0
• D. pH 4.0

Answer: (B)

Alcian Blue staining depends on the charge of acidic mucopolysaccharides. The dye is positively charged and binds to negatively charged groups, so whether carboxyl or sulfate groups are ionized at a given pH determines what is stained. At pH 2.5, both sulfated and carboxylated mucopolysaccharides carry negative charges, allowing Alcian Blue to bind to carboxylated acid mucopolysaccharides and reveal them. If the pH is reduced to 1.0, carboxyl groups become protonated (no negative charge) and won’t bind the dye as effectively, so staining mainly reflects sulfated mucopolysaccharides. Higher pH values can change which groups are ionized and alter the staining pattern away from highlighting carboxylated mucopolysaccharides. Therefore, the pH that demonstrates carboxylated acid mucopolysaccharides is 2.5.