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: METHODS : We prospectively evaluated the safety of coronary CTA for low - risk patients who presented to the ED with cocaineassociated chest pain ( self - reported or positive urine test ) .
### Output Text:
METHODS : We prospectively evaluated the safety of coronary CTA for low - risk patients who presented to the ED with cocaineassociated chest pain ( self - reported or positive urine test ) . 