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: A single 18 . 4 mg / kg ( i . p . ) dose of ( + / - ) - amphetamine hemisulfate , given to rats pretreated with iprindole , resulted in persistent depletion of dopamine in the striatum 1 week later .
### Output Text:
A single 18 . 4 mg / kg ( i . p . ) dose of ( + / - ) - <span class="chemical">amphetamine</span> hemisulfate , given to rats pretreated with <span class="chemical">iprindole</span> , resulted in persistent depletion of <span class="chemical">dopamine</span> in the striatum 1 week later . 