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: Graded dobutamine infusions of 0 . 5 , 2 . 5 , 5 and 10 micrograms / kg per min were administered .
### Output Text:
Graded <span class="chemical">dobutamine</span> infusions of 0 . 5 , 2 . 5 , 5 and 10 micrograms / kg per min were administered . 