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: Patients received amifostine , 910 mg / m2 intravenously over 15 minutes .
### Output Text:
Patients received <span class="chemical">amifostine</span> , 910 mg / m2 intravenously over 15 minutes . 