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: In the evening of postoperative day 1 , patients were evaluated for TNSs by a physician unaware of the drug administered and the details of the anesthetic procedure .
### Output Text:
In the evening of postoperative day 1 , patients were evaluated for TNSs by a physician unaware of the drug administered and the details of the anesthetic procedure . 