Periodic acid (H5IO6) is frequently used in the P.A.S. P.A.S.(Periodic Acid Schiff) method used for staining aldehydes, mucopolysaccharides and mucoproteins in purple/magenta. In case the acid mucosubstances (glycosaminoglycans) must be detected, Alcian Blue dye in Alcian-P.A.S. staining method can also be used (besides Schiff’s reagent and periodic acid).