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: A randomized , placebo - controlled , crossover study of ephedrine for SSRI - induced female sexual dysfunction .
### Output Text:
A randomized , placebo - controlled , crossover study of <span class="chemical">ephedrine</span> for SSRI - induced female sexual dysfunction . 