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 study examined the effect of alpha - tocopherol ( alpha - TC ) , a scavenger of reactive oxygen species , and deferoxamine ( DFO ) , an iron chelator , on the MA - induced neurotoxicity .
### Output Text:
This study examined the effect of <span class="chemical">alpha - tocopherol</span> ( <span class="chemical">alpha - TC</span> ) , a scavenger of reactive <span class="chemical">oxygen</span> species , and <span class="chemical">deferoxamine</span> ( <span class="chemical">DFO</span> ) , an <span class="chemical">iron</span> chelator , on the <span class="chemical">MA</span> - induced neurotoxicity . 