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 purpose of the present study was to examine the safety and efficacy of ketamine for sedation in the treatment of children ' s fractures in the emergency department .
### Output Text:
The purpose of the present study was to examine the safety and efficacy of <span class="chemical">ketamine</span> for sedation in the treatment of children ' s fractures in the emergency department . 