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: dl - Sotalol preferentially prolonged action potential duration ( APD ) in M cells dose - dependently ( 1 to 100 micromol / L ) , leading to QT prolongation and an increase in TDR .
### Output Text:
dl - <span class="chemical">Sotalol</span> preferentially prolonged action potential duration ( APD ) in M cells dose - dependently ( 1 to 100 micromol / L ) , leading to QT prolongation and an increase in TDR . 