In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: The heparan sulphate specificity of the cuprolinic blue staining was demonstrated by glycosaminoglycan - degrading enzymes , showing that pretreatment of the sections with heparitinase abolished all staining , whereas chondroitinase ABC had no effect .
### Output Text:
The <span class="chemical">heparan sulphate</span> specificity of the <span class="chemical">cuprolinic blue</span> staining was demonstrated by <span class="chemical">glycosaminoglycan</span> - degrading enzymes , showing that pretreatment of the sections with heparitinase abolished all staining , whereas chondroitinase ABC had no effect . 