Alcian Blue is a basic dye that has an affinity for acidic tissue elements like mucin. The dye gets its color from the copper in the molecule.
The pH of the Alcian Blue staining solution is a critical factor in the staining procedure and has a direct effect on the category of mucins that can be demonstrated with the procedure. The pH of Alcian Blue staining solutions should range from 0.4 to 2.5.
Alcian Blue solution with a pH of 1.0 is capable of staining most sulfated acid mucins. These mucins can be found in cartilage, large intestine goblet cells and bronchial serous glands. An alcian blue pH 1.0 stain can be seen in the top image.
Alcian Blue solution with a pH of 2.5 is capable of staining carboxylated mucins in connective tissues and cartilage. It is also capable of staining some weakly sulfated acid mucins like those in cervical tissue. An alcian blue pH 2.5 stain is shown in the bottom image.