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: In 1 session , tropicamide ( 20 microL , 0 . 01 % ) was administered to one eye and placebo to the other .
### Output Text:
In 1 session , <span class="chemical">tropicamide</span> ( 20 microL , 0 . 01 % ) was administered to one eye and placebo to the other . 