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: RESULTS : Methadone dose was associated with longer QT interval of 0 . 140 ms / mg ( p = 0 . 002 ) .
### Output Text:
RESULTS : <span class="chemical">Methadone</span> dose was associated with longer QT interval of 0 . 140 ms / mg ( p = 0 . 002 ) . 