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: Those patients in whom d , l - sotalol prevented induction of ventricular tachycardia or ventricular fibrillation were discharged with the drug and followed up on an outpatient basis for 21 + / - 18 months .
### Output Text:
Those patients in whom <span class="chemical">d , l - sotalol</span> prevented induction of ventricular tachycardia or ventricular fibrillation were discharged with the drug and followed up on an outpatient basis for 21 + / - 18 months . 