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: OBJECTIVE : This large - scale retrospective review evaluates the sedation profile of dexmedetomidine .
### Output Text:
OBJECTIVE : This large - scale retrospective review evaluates the sedation profile of <span class="chemical">dexmedetomidine</span> . 