Which color does the colloidal iron demonstration show for acid mucopolysaccharides?

• A. Blue
• B. Red
• C. Purple
• D. Green

Answer: (A)

The test targets sulfated (acid) mucopolysaccharides by using colloidal iron, which binds to the negatively charged sulfate groups. When the iron complexes form and are developed, they produce ferric ferrocyanide, known as Prussian blue. That blue reaction specifically marks areas rich in acid mucopolysaccharides, while neutral mucopolysaccharides don’t produce this blue with colloidal iron. So the color you see indicating the presence of acid mucopolysaccharides is blue.