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: The analysed carbachol concentration exceeded the supposed serum level resulting from a therapeutic dose by a factor of 130 to 260 .
### Output Text:
The analysed <span class="chemical">carbachol</span> concentration exceeded the supposed serum level resulting from a therapeutic dose by a factor of 130 to 260 . 