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: CONCLUSIONS : During induction of anaesthesia with TCI of propofol and remifentanil , a significant reduction in propofol infusion pain was achieved without significant complications by prior administration of remifentanil at a target Ce of 4 ng ml ( - 1 ) .
### Output Text:
CONCLUSIONS : During induction of anaesthesia with TCI of <span class="chemical">propofol</span> and <span class="chemical">remifentanil</span> , a significant reduction in <span class="chemical">propofol</span> infusion pain was achieved without significant complications by prior administration of <span class="chemical">remifentanil</span> at a target Ce of 4 ng ml ( - 1 ) . 