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: Therefore programmed electrical stimulation in the case of d , l - sotalol seems to be of limited prognostic value .
### Output Text:
Therefore programmed electrical stimulation in the case of <span class="chemical">d , l - sotalol</span> seems to be of limited prognostic value . 