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: However , the threshold ( 61 . 6 + / - 8 . 7 mg . l ( - 1 ) ) during 1 . 6 % sevoflurane was not significant from that during 0 . 8 % sevoflurane , indicating a celling effect .
### Output Text:
However , the threshold ( 61 . 6 + / - 8 . 7 mg . l ( - 1 ) ) during 1 . 6 % <span class="chemical">sevoflurane</span> was not significant from that during 0 . 8 % <span class="chemical">sevoflurane</span> , indicating a celling effect . 