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: Detailed spectral profile analysis of penicillin - induced epileptiform activity in anesthetized rats .
### Output Text:
Detailed spectral profile analysis of <span class="chemical">penicillin</span> - induced epileptiform activity in anesthetized rats . 