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 the ' conscious catheterized rat ' model , the glomerular filtration rate ( GFR ) was measured as the clearance of Cr ( EDTA ) .
### Output Text:
In the ' conscious catheterized rat ' model , the glomerular filtration rate ( GFR ) was measured as the clearance of Cr ( EDTA ) . 