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: This study prospectively evaluated the clinical efficacy , the incidence of torsades de pointes , and the presumable risk factors for torsades de pointes in patients treated with d , l - sotalol for sustained ventricular tachyarrhythmias .
### Output Text:
This study prospectively evaluated the clinical efficacy , the incidence of torsades de pointes , and the presumable risk factors for torsades de pointes in patients treated with <span class="chemical">d , l - sotalol</span> for sustained ventricular tachyarrhythmias . 