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: We studied whether a negative coronary CTA in patients with cocaine - associated chest pain could identify a subset safe for discharge .
### Output Text:
We studied whether a negative coronary CTA in patients with <span class="chemical">cocaine</span> - associated chest pain could identify a subset safe for discharge . 