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: l ( - 1 ) when the end - tidal concentration of sevoflurane was 0 . 8 % .
### Output Text:
l ( - 1 ) when the end - tidal concentration of <span class="chemical">sevoflurane</span> was 0 . 8 % . 