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: Thirty - nine received coronary CTA after a brief observation period , with 37 discharged home following CTA ( 95 % ) .
### Output Text:
Thirty - nine received coronary CTA after a brief observation period , with 37 discharged home following CTA ( 95 % ) . 