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: This was most frequently found in children , many of whom had received clioquinol as treatment for acrodermatitis enteropathica .
### Output Text:
This was most frequently found in children , many of whom had received <span class="chemical">clioquinol</span> as treatment for acrodermatitis enteropathica . 