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: METHODS : A series of tests on various parameters of visual function and driving simulator performance were performed on 12 healthy drivers , before and after pupil dilation using guttae tropicamide 1 % .
### Output Text:
METHODS : A series of tests on various parameters of visual function and driving simulator performance were performed on 12 healthy drivers , before and after pupil dilation using guttae <span class="chemical">tropicamide</span> 1 % . 