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: At various time intervals , physical examination and blood collection for ex vivo platelet aggregation and determination of intraplatelet cAMP were performed .
### Output Text:
At various time intervals , physical examination and blood collection for ex vivo platelet aggregation and determination of intraplatelet <span class="chemical">cAMP</span> were performed . 