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 clinical evaluation of etomidate for outpatient cystoscopy was embarked upon .
### Output Text:
A clinical evaluation of <span class="chemical">etomidate</span> for outpatient cystoscopy was embarked upon . 