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: A paracetamol serum level obtained in one of these patients was not in the toxic range .
### Output Text:
A <span class="chemical">paracetamol</span> serum level obtained in one of these patients was not in the toxic range . 