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: Plasma was tested for amphetamine and the cocaine metabolite benzoylecgonine using enzyme - mediated immunoassay methodology .
### Output Text:
Plasma was tested for <span class="chemical">amphetamine</span> and the <span class="chemical">cocaine</span> metabolite <span class="chemical">benzoylecgonine</span> using enzyme - mediated immunoassay methodology . 