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: Seventy - one participants completed 2 separate study days and were blind to medication condition ( placebo , 10 - mg oxycodone ) .
### Output Text:
Seventy - one participants completed 2 separate study days and were blind to medication condition ( placebo , 10 - mg <span class="chemical">oxycodone</span> ) . 